A little late getting back to this (was away from HN this weekend), but some things do use color changes and background changes to alert the user. There's also

A little late getting back to this (was away from HN this weekend), but some things do use color changes and background changes to alert the user. There's also audio tones for various things, like the autopilot being disabled (regardless of whether the computer or user disabled it). The actual sounds depend on the features installed; a GFC700 autopilot has different sounds and alerts than a KAP140. If you're interested in human factors in aviation, there's a lot of work being done out there in the field. A friend of mine is actually working on an MS in Human Factors at ERAU.