I have a door that swings open quite fast, and we need a sort of decorative strip that can go on the wall to prevent the door handle from banging into it. The problem is that we need to be able to paint over the material used, so it will look like the rest of the wall. I'm not sure if this is even possible, as I can't seem to find anything about it.
If you have cement walls and you're trying to protect the doorknob, I'd look at EVA foam, which you could paint to match the wall (although it wouldn't be invisible).
If what you are trying to protect is the wall (drywall), there are various resilient wall protectors you can buy or make, but I've yet to find a really satisfactory solution via putting something on the wall. I've even seen a big rubber doorknob catcher "cup" get punched into the wall, making a huge hole when it got slammed.
Things that are relatively effective for protecting drywall can be hard to hide. In a commercial or industrial setting, a large, heavy-duty metal plate is sometimes used, but those could damage a non-industrial doorknob. A metal plate will spread the force over a large area and would probably be the thinnest material; a large square of high-pressure laminate might also work. You can paint either of those, but any finish is likely to chip off when beat on by a doorknob. With high-pressure laminate, you might find a laminate sample that would blend in.
The best solution I've found is to use hinge-mounted stops. You pull out a hinge pin and reinsert it through a stop.
Depending on the hinge, you may be able to use something like this that works entirely inside the hinge:
If that type isn't compatible with your hinge, this type will normally work:
If the door gets serious abuse, this style can eventually leave a dent in the wood it presses against. The type with a large rectangular pad (as shown), is less likely to leave a dent than the type with a round bumper on each side. You can also reduce the chance of getting a dent if you put a stopper on several hinges so the stress on each one is reduced (just adjust them to make contact at the same time).
Otherwise, a doorstop that mounts on the baseboard molding and catches the bottom of the door will work better than something wall-mounted to catch the doorknob, and will be less noticeable.
All of the hinge-mounted or baseboard-mounted doorstops are available in a variety of finishes to blend in. So you generally don't need to paint them, although you could.