If you're looking for a fun and fast game to test your recollection of mixing primary and secondary colors, Mixt [App Store] should do the trick. Like most good puzzle games, the premise of the game is simple but gets challenging quick.
In Mixt, blobs of colors fall from the top of the screen. They can be controlled by touching and dragging your finger to send them flying in whatever direction you choose. When two blobs collide, if they're the same color, they combine and grow in size. If they're two different colors, they mix together. At the bottom of the screen is a series of colored pools that blobs of corresponding color need to get dropped in to. If you need to break a mixed blob, swiping across one will break it in to the two original blobs that were combined.
Things quickly get difficult as there isn't always a color pool at the bottom of the screen that matches the blobs you're juggling. For instance, sometimes there just won't be a yellow pool and you're forced to mix yellow in to green or orange to match it to a pool. Here is a video showing the game's tutorial, and here is a video of what the game looks like once you're actually playing:
Another game worth considering is Anthropophagy's Stay [App Store], a physics-based balancing game. In Stay, a red shape appears on a beam and touching she screen drops another block to balance the beam from tipping. You want to keep the special red shape, or your "friend" as the game calls it, on the beam for as long as possible.
It's not as simple as it sounds though, because when you touch the screen you have no control over what type of block gets created. You might just get a normal block, a block that pops in to a larger shape, or a block that explodes among others. Surviving any more than a few seconds on the harder difficulty levels usually is just the result of frantic tapping and doing everything you can from dumping all the blocks off the beam.
The developer released this excellent gameplay video that shows exactly what I'm talking about:
Both are relatively simple games but high quality productions so if either of the videos look interesting to you, they are worth considering.
App Store Links: