Section 508 sets the (US) government's standards for accessibility on web sites as well as applications. Contrast is specifically called out in two sections of the quick start guide:

1. 1194.21 (g) Applications shall not override user selected contrast and color selections and other individual display attributes.

2. 1194.21 (j) When a product permits a user to adjust color and contrast settings, a variety of color selections capable of producing a range of contrast levels shall be provided.

See: http://www.section508.gov/content/learn/standards/quick-refe...