Seems kind of easy. But there are some very interesting problems here. You will have to mix red & blue to get purple, then knock it out with yellow. Got that? Watercolors has some very interesting color topology problems that seem impossible, but are doable - if you knock secondary colors out.
There are 45 levels with 3 colors. I've solved 42 of them. Again, using lots of extra moves.
There is a 'Grid Pack' with another 45 levels. I've done 20 of them.
Beyond that, there are several more packs with very challenging levels. I have not unlocked those because I'm not done with the 3 Colors pack.