The iPhone is a great platform for colorfull puzzle and reflex games. Here is just a little advice to anyone developing such a game right now.
★★★
If distinguishing different colors is essential to the gameplay, also think of people who are color blind! ★★★
I'm not colorblind myself, but a while ago a colleague mentioned that one of my older games was unplayable for him, because he is color blind. Ever since then, I've been noticing that actually many games simply do not take this into account. Color blindness affects about 1 out of 20 men (5%), so this is a significant part of your potentional gaming audience. So I'd say it's worth the effort of tailoring your app also for people who are color blind, especially because usually it's very little effort at all.
Simply distinguish the tiles or enemies (or whatever) by optionally adding numbers or letters or symbols, in addition to the colors. Or have them filled with different patterns, like stripes or dots or waves etc.
See for example this image from the article
Color-blind gamers: common. Developer awareness? Minimal
Super Puzzle Fighter II Turbo as seen by someone with normal eyes and by someone with Deuteranopia (a red-green color deficit)
I've been noticing a lot of new games here that are not accessible for color blind gamers. Instead of posting in each one of these (and possibly future) threads, I'd though I start a separate thread about it.