iPhone RGB values are from 0 to 1. Using something like (0, 0, 255) gives no warnings what-so-ever. Just silently accepts whatever values you give it and happily tries its best to show you - WHITE !!!
As a sample, here's beige color:
myView.backgroundColor = [UIColor colorWithRed:0.96 green:0.96 blue:0.86 alpha:1];
Please note that alpha value 0 (zero) means transparent. If your alpha is 1 (one), you will see color of object below your component, regardless whether you used correct RGB values or not.
That wasn't happy debugging at all.