I solved the first 3 puzzles. I think this is particularly difficult for me because I can't even name these colors. Aqua-Marine? Teal? Greenish-Gray?
Look at the very bottom of the second image. See the tiny question mark? Tap on that and it will tell you which of the Big Circles have already matched the Target Color.
There are 120 levels. The first 10 are free. The rest cost $1.99