Can anyone tell me what type of crochet stitch is being used here in the light green area (above the pink on the wrist).
It looks like possibly 3 dc stitches in one hole, but I'm wondering if anyone knows more?
Looks like a double crochet three together (dc3tog).
It's commonly used as a decrease stitch but in this case there are likely a chain or two on each side leaving the space for the two maroon single crochets.
It looks like a complex stitch but it's really just three unfinished half crochets that then get finished all at once. Working through it once or twice should be all you need if you're comfortable with double crochets in general.
Step 1: Yarn over.
Step 2: Take tip of hook insert into next st in row.
Step 3: Yo hook and draw yarn through st. (3)
Step 4: Yarn over and draw through two loops on hook.
Step 5: Yarn over.
Step 6: Take tip of hook insert into next st in row.
Step 7: Yo and draw through stitch.
Step 8: Yarn over and draw through two loops on hook.
Step 9: Yarn over.
Step 10: Take tip of hook insert into next st in row.
Step 11: Yo and draw through once more (5 sts on hook).
Step 12: Yo and draw through 2 loops on hook (4sts on hook).
Step 13: Yo once more and draw through all 4 sts on hook.
The link above also includes a video tutorial.
Note, that for the pattern above, steps 6 and 10 would be the same space rather than the next stitch as they're being worked in a chain space rather than in stitches.
I think it is a bit more complex than three double crochets in one stitch--but that is the foundation.
Working from the edge of the sleeve towards the body, it appears to me that the edge was created by:
Starting the Sleeve
The next round is where you are going to be doing the 3 double crochets in one.
Sleeve Round 1
Sleeve Round 2
Alternate Sleeve Rounds 1 and 2 until the sleeve is the length that you need.
However, because a sleeve has to get wider as it goes up the arm, you will have to experiment with increasing the diameter by gradually adding more chain stitches in step 3 of sleeve round 1.
Determining how many stitches to add, and how often to add them will be determined by your specific gauge.
How many stitches to add: Let's say that your gauge is three stitches per inch, you will need to add three stitches to one round to increase the diameter by one inch. One way to do this is to work Sleeve Round 1, Step 3 normally, except--three times, evenly spaced around the circle, you will work chain 3 instead of chain 2. When you work Sleeve Round 2, Step 1, work three single crochets into those Chain 2 sections. Your entire sleeve circumference will now be an inch wider.
To determine how often to increase: You can figure out how often to do this type of increase by measuring the height of a Round 1 and Round 2 pair. Let's say that the height of these two rows together equals 1 inch.
Keep in mind this is all just guesswork on my part. @Catija has provided another possible answer to how this fabric was created. The best option is for you is to work a sample using her pattern and a sample using my suggestion and see which version seems to come closer to recreating the fabric in your image.