JavaScript ColorPicker
This colorPicker is a light weight all-rounder (~ 29kB - only 1 file*; 12.8kB gZiped) that can display and let you choose the entire color palette in HSB and RGB color modes. This highly customizable, easy to install and speed optimized app comes in 4 different sizes (from 151 x 87 pixels to 407 x 302 pixels) and therefore different feature levels so you can use it for every supposable cause from 'easy choice' to 'professional determination'. That's probably all you'll ever need to let your clients choose the right color. You'll also find a lot of extra helpers and smart features that make life easier.