Testing websites for accessibility may be commonplace for some. Still. Even those who follow accessibility guidelines seem to have difficulties with color. Web Content Accessibility Guidelines 1.0, Guideline 2. Don't rely on color alone. is sometimes difficult to "visualize".
When designing sites, I will develop mock-up comps in Photoshop based on client requirements and all of those things web standards proscribes including accessibility features. Static colors are simple; Channel Mixer>Monochrome will show contrast of the colors. Rollovers are difficult. Clients may want rollovers based on a fixed color palette; fixed color palettes—Often—do not lend themselves to an acceptable contrast of rollover states. Long, frustrating discussions often ensue.
Accessibility testing has been simplified.
Graybit I found on Beast-Blog.com | Mike Cherim’s Professional and Personal Web Log.
GrayBit is an online accessibility testing tool designed to visually convert a full-color web page into a grayscale rendition for the purpose of visually testing the page’s perceived contrast.
Two features are exceptional. Sites are shown gray. And, Graybit's PHP technology allows for meanderings around sites and never leaving Graybit, i.e., “php?url=”
It's interesting viewing sites in grey.