Articles on Colour

UK Builder
Colourful Language: Guidelines on using colours in user interfaces
Make the Right Colour Choices

Giacomo Mazzocato's The Accessibility Color Wheel
Neat code that lets you instantly view samples, and also checks for deuteranopia (insensitivity to green), protanopia (insensitivity to red), and tritanopia (insensitivity to blue).
[Contributed by Eric Novins]