colour mixing for a still life with apples

Question

As a beginner hobbyist painter (using acrylics at the moment), I am trying to learn the basics and do some practice, and found the videos made by a US guy ('Paint Coach') very instructive.

I have 2 questions regarding this video, where a still life with 3 green apples on a pink background is suggested as a way to study colour transitions, shadows, reflected light etc.

1. Does it make sense to attempt this using acrylics, although it's originally done in oil?
   My idea was that the exercise was mostly about learning about values, hues, etc. than about oil per se or about getting a painting exactly matching the instructor's one. Just checking with you if my assumption is correct or not.

2. How would you go about mixing the various colours for the apples (using acrylics)?
   I tried it out earlier today :), and my main issue was the colour mixing part, especially for the apples (more optional details/explanations below).

Using the advised blocking method, I had to mix first a dark green and a light yellow-green.
That however resulted in the former being more a dull olive green, and the latter a much more vibrant and too light green.
From there it was all very challenging to lighten and darken the colours to make the 'in-between' shades.
To make things worse, the paint, being acrylic, started filming and drying on the palette, so I could not inter-mix, ended up making some more greens and getting even more 'off' hues.
In essence, the result was very noisy and lacking harmony, with bright, cold greens next to dark, warm ones, really fighting each other instead of looking like they belonged together.
So I wonder if the trick that I missed was to make some sort of initial 'reference' green, to darken and lighten more conservatively, to maintain some harmony and coherence in the final palette.

In fact, I can show that Krita identifies just a limited and more harmonious set of colours in the reference photo (I set the max to 20).

Would I be able to make all these colours by making only some of them first, and then branch out by inter-mixing or dulling/lightening?

Another thought/doubt: perhaps this exercise was too hard for a complete beginner? Maybe I should have started with a simple sphere lit from one side, without reflected light, trying to give it form and volume by lightening and darkening only one basic colour.
Or would that be wrong, too, meaning, would I still need to mix rather different hues to start with and do a lot of inter-mixing and transitions?

For reference, I watched these two IMO very nice videos regarding colour mixing, and I learned a lot from them (but clearly then I still do not know what I must do exactly in practice):
https://www.youtube.com/watch?v=xQYcG4Km1-k
https://www.youtube.com/watch?v=DYGi18U4D4M

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EDIT

Found something using Krita, which may (partly) answer my question 2.
When you pick a colour from the reference image, Krita's 'Advanced Colour Selector' shows you where it is located in a HSV map.

If I understood correctly what this tells me, it looks as though, for all the apparent complexity of the green apples still life I am discussing here, all the greens are just different tints or shades of about the same yellow-green hue, and all the pinks, including the shadows, come from the same rather pure red hue. The only exception is the reflected pinkish light on the apples, which sits more in a yellow-orange hue.

Here are some pictures:

• sampling from the top of an apple
  
• sampling from the lighter part of the shadow on the pink background
• sampling from the reflected light
  

The little line you see on the hue wheel almost does not move when I stay in the same 'object', only the dot moves around inside the triangle.
I am interpreting this as in: you can get all the apple greens by lightening or darkening a basic yellow-green.

Assuming this is the case, the question will be if I am able to do it in practice, mixing actual colours from tubes.
For this reason, my question 2 is still not fully answered: I do not know if this strategy is correct or if it would work in practice, in particular with acrylics.

In fact though, even before finding out the above, that's what I had done for the pink background and its shadows: I took some magenta, added some primary yellow to shift it towards red, lightened with titanium white for the lighter parts, and darkened it (with considerable difficulty and trial+error) with primary blue + primary yellow for the shadows.

One thing is certain: nowhere in the reference image do I find the cold, bluish greens I had used in my first attempt, perhaps explaining why I found the result so odd and lacking harmony.

Answer 1

In my personal opinion, the video tutorial is really good and valuable for beginners, but as you noticed yourself, acrylic paints behave differently and require a different painting method.

First my thoughts about the tutorial: everything he says about composition and simplification, brushstrokes, hues and values is correct for both acrylic and oil paintings. All of it is important to really understand and internalize for any artist who wants to improve their paintings. Unfortunately he cannot go into detail in such a short video, so maybe look for additional tutorials about each individual topic.

The one thing that is not applicable to acrylic paints is the visual part where you see him actually painting the apples. Oil paints need a very long time to dry so it's easy to mix different paints directly on the canvas (wet on wet). Acrylic paints dry too fast for that and you mostly need to mix wet on dry, which requires you to apply several slightly transparent layers instead of one fully opaque one.

Maybe this tutorial by Drawing & Painting - The Virtual Instructor is more helpful. It's also about painting an apple, but with acrylic paints. The author describes the meaning of an underpainting (painting only the value, not the hue) and how to gradually build up the apple from a very simplified first layer of hues to adding gradually more details and depth to the colors. You'll find many parallels to your original oil painting tutorial, but applied in a way that's more relevant to acrylic paints.

Now to the clashing colors: If you start your painting with clashing base colors, you always create stark contrasts, a "noisy" painting that many describe as having a "high energy" and lacking harmony. It feels agitating instead of calming.

As you already suspected, you should start your painting with a single base tone for each object. One base green for the apples and one base pink for the background. It should be a medium brightness relative to points of light reflections and shadows. You don't have to use a single base tone from a tube of paint, you can mix it, but you should limit yourself to a mix of 2 paints.

From there you can lighten up the paint by mixing it with bright yellow (or a mix of yellow and white) or a lighter color of the same tone (like a lighter green). You can darken it by mixing it with brown (for warm colors), dark blue (for cold colors) or a classic mix of Prussian blue, madder red and chrome oxide green. You can decrease the saturation by mixing it with white, black or grey. And you can "break" or mute the color by mixing it with the opposite on the color wheel (this one actually has a tendency to contrast or clash with the base tone).

Look at the lower left corner of the oil painting tutorial at 2:30. You see the palette with the medium green used for the first blocks of green on the apples. At 2:42 you see the lighter green is mixed by adding a big blob of yellow to the first base tone. From 3:09 - 3:20 you see more and more small blobs of colors touching the base green and being mixed with it. That way you can create a great number of colors that are much more likely to harmonize with each other. You also give yourself a chance of achieving very similar tones from the same limited number of paints after the first batch dried on your palette.

My tip for keeping your paints wet is using a "wet palette". It's a sponge in a water filled container, topped with a sheet of water-resistant paper. I myself crafted such a wet palette from an empty plastic food container, a cheap sponge I cut to size and some parchment paper for baking. The greased baking paper doesn't allow the water to soak into the paints, it has to be parchment paper because that is still slightly water-permeable. Eventually the paper will disintegrate and it can even mould if left for too long, but it's a great help for keeping acrylics from drying out during a painting session.

Answer 2

Does it make sense to attempt this using acrylics, although it's originally done in oil?

It does. The video is mostly theoretical to begin with, and breaks up painting a still life (and, as the creator keeps emphasizing, any subject) into very useful, basic steps: composition, rough outlining, simplifying shapes and using flat planes to quickly create an overall impression, direction of strokes, and the importance of values.
These are all equally important for painting as well as drawing.
Regarding your doubts ("perhaps this exercise was too hard for a complete beginner? Maybe I should have started with a simple sphere lit from one side [..]?): I don't believe it is too hard, and I think your main problem was just that the colour mixing didn't work out for you (which I believe is at least for a great part a technical problem—see below). A sphere is actually really hard to paint, as you need a lot of smooth transitions, and a very exact positioning of the reflections and shadows for it to look right. It would still be a great exercise, though, but I think one you should first attempt in charcoal or pencil (the first being more painterly and intuitive to work with).

How would you go about mixing the various colours for the apples (using acrylics)?

More so than oils, cheap/student-grade acrylic paints can be hard to mix properly, because they are chromatically not very pure. Some contain a lot of filler (and/or opacifiers and/or dyes), making them mix poorly with each other, as well as with other acrylic paints with less filler, as the ratios we assume would work won't. It also desaturates colours.

I would suggest getting a large range of student-grade colours, or invest in higher quality acrylic paints (preferably without any filler).
In the first scenario, you look for colours that most resemble the target colours, and mix in less additional colours to adjust them. In the second scenario, mixing should be a lot more straightforward and intuitive.

Would I be able to make [the colours below] by making only some of them first, and then branch out by inter-mixing or dulling/lightening?

Yes, you would.
I see three basic hues here: a pink, a green, and a grey. The first two can be seen in the middle of the top row; the purest grey is the first colour depicted.
The browns can be mixed using these three hues, but you might want to use a dark brown to darken the other hues, and a white to do the opposite.

Using the advised blocking method, I had to mix first a dark green and a light yellow-green.
That however resulted in the former being more a dull olive green, and the latter a much more vibrant and too light green.
From there it was all very challenging to lighten and darken the colours to make the 'in-between' shades.

Always make sure the first, basic colours you mix are right; don't try to fix muddy colours by bringing in other colours, as this will only make them muddier.

To make things worse, the paint, being acrylic, started filming and drying on the palette, so I could not inter-mix, ended up making some more greens and getting even more 'off' hues.

Apart from the method Elmy describes in her answer, the "wet palette", you can use a retarder to slow down the drying while working, or put plastic film over your palette in-between sessions. You can also place it in the fridge to slow the process down even more (keeping the acrylic paint fresh for months).

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Your (incisive) colour wheel experimentation conclusion is spot on: within the separate objects depicted, only the value really changes. By dragging the small circle within the triangle to the lower right corner, you find the pure value you should use for painting these objects.
For the apple, for example:

(Nitpicking here, but do note that the reference image used is based on a photo in a video: that's two steps removed from the actual real-life subject, which, naturally, has a lot more colour depth and richness to it.)

You might also find it useful to know that almost every material, no matter how matte and/or dark, reflects adjacent colours. I find realizing this, and seeing this in the world around me, really helps me depict objects in the same space. The apple reflects the surface it rests on, so for painting that part of the reflection, you'll need to mix in a little of the basic colour of that surface (the pink). This will immediately 'ground' the apple within the picture space.
(The effect of lighting is actually the exact same process, but since a light source is usually very bright, we tend to think of it as a 'whitening' of the colour, whereas, in fact, it is reflection of the same kind.)