We created a special version of Fruit Ninja used in hospitals to help recovery and hand-eye coordination. They asked us to put in options to make the background a single colour and make the fruit have big outlines.
Steven Last, via Twitter

Judging which elements are interactive and which aren’t can be a significant issue for some people, who may not understand the same metaphors and conventions as others. If developing for more profound cognitive impairments consider removing all background elements. The backgrounds however may still be of great benefit to other players within the same demographic, so allowing them to be turned on/off via settings will allow both groups to benefit.

Best practice example: Shoot1Up
Best practice example: Something Special: Out and About
Best practice example: Street Fighter IV