ColorUtils is a category on UIColor that extends it with some commonly needed features that were left out of the standard API.
UIColor is a thin wrapper around CGColor, which supports a wide variety of different formats, making it very flexible. This flexibility seems to come at a bit of a cost to usability for common tasks however. For example, it's non-trivial to access the red, green and blue components of an RGB color, and it is difficult to compare colors because [UIColor blackColor] is treated as different from[UIColor colorWithRed:0 green:0 blue:0 alpha:1] even though they are identical on screen. ColorUtils makes this tasks easy.
Another common problem is that RGBA UIColors are specified using four floating point values in the range 0 to 1, but virtually all graphics software treats colors as having integer components in the range 0 - 255, often represented as a hexadecimal string. ColorUtils lets you specify colors as hexadecimals so you can copy and paste values directly from PhotoShop.