iOS's UIColor class makes it pretty easy to specify a color using red, green, blue (RGB) and alpha components:
// set pale yellow color
label.textColor = [UIColor colorWithRed:1.0
green:1.0
blue:0.5
alpha:1.0];
However, as with many Cocoa API's, it's pretty verbose. Web developers would specify that color using the hexcode shorthand #ffff80, and many graphics editing tools would generate a hexcode value like that rather than values in the range 0.0–1.0.
So I made a simple category on UIColor that lets one write stuff like this:
#include "UIColor+KDJPackedRGB.h"
// ...
// set pale yellow color
label.textColor = [UIColor colorWithRGB24:0xffff80];