Color Picker for iOS
Source includes two controls that work in unison with each other to provide users the ability to pick color in a fashion identical to photoshop.
Designed not to use images or any other external dependencies beyond the classes.
This control presents a saturation and brightness gradient for a specific hue, similar to photoshop's color picker.
This control presents a horizontal gradient that displays the entire range of hues. Typically, user would pick a hue, which updates an ILSaturationBrightnessPicker so that they can then pick the saturation and brightness.
This category will allow you to access the HSB values of a UIColor easily.
This is the base view that implements some stuff to make writing custom views a little easier.
See the enclosed example project. It's pretty straight forward.
Public domain, use as you wish.