Color and Contrast
Check out this really nice site about color and contrast. It's got lots of information about, well.. color and contrast. But, it also has information about how these things impact the people we're designing for. It's "a comprehensive guide for exploring and learning about the theory, science, and perception of color and contrast."
This website is for designers to learn about color, contrast, and how it can affect experiences of a user interface. It provides quick access to relevant information at any point in the design process. - Nate Baldwin