I had a Game Boy once. I could play it just about anywhere, and battery life - for the time - was great. I lost it at one point, and replaced it with a Game Gear, which sucked the life out of 6 AA batteries rather quickly. The Game Boy Color was actually decent on battery life, but since it didn’t have a backlight, you had to play it at very specific angles.
For gaming, I can appreciate the need for a color screen. My point has to do with cellphones. True, most cellphones today come with cameras, are able to play video, and are rather capable mobile gaming platforms (when compared to the Game Boy, that is). All this does, in fact, require a color screen. However, I believe that there is a market for cellphones which do not support these features, but do support neat things like 3G internet connectivity (GMail and RSS on the phone is a major Win, in my opinion), and have a comfortable SMS interface. These features actually suffer from having a color screen: Battery life (for the powerful backlight), viewing angle, and screen resolution take a hit. While it’s true that color LCDs have come a long way since the Game Gear, so have black & white display technologies (E-Paper, anyone?).
Of course, my wish for a modern B&W-screen cellphone will likely never come true. The simple reason is that they would be totally unmarketable. Even business-types like color screens nowadays. So I’ll just keep holding out for a folding E-Paper mobile browser.