VSTS originally used intuitive colors for code that was covered, code that was not covered, and code that was partially covered. In beta 2, these was changed to a bunch of pastel colors, as others like Dave Donaldson notes. Dave explains how to switch this back to the more obvious primary colors:

To do this, go to Tools, Options, Environment, Fonts and Colors. Under the Display Items list, look for Coverage Not Touched Area, Coverage Partially Touched Area, and Coverage Touched Area. Then change the Item Background color for each of those as you see fit.