Yet another good example of how to use libraries bundled with Jetpack on your site!
My colleague Konstantin Kovshenin recently released the Semicolon theme. It uses the libraries used in Jetpack’s Custom CSS module to compile its stylesheet (yay Sass!), and to correct the contrast of the colors you’ve picked in the theme options. So if you pick bad contrasting colors, Semicolon will lighten or darken them until a contrast ratio threshold is reached. This guarantees a certain level of readability.
You can read more about it in Konstantin’s post: Color Options vs. Decisions in WordPress Themes.