Here’s a very nice new tool for checking color contrast against WCAG 2.0 standards for accessibility. It was created by Lea Verou and is called Contrast Ratio.
The tool allows you to swap text color and background color. It permits the use of transparency in both text color and background color. If your color choices fail to meet the WCAG 2.0 standards, the ratio button in the middle of the page turns red. Hovering over the button tells you how many, if any, of the WCAG 2.0 standards your colors meet.
Bump up the level of opacity a bit on this color scheme and it passes.
Directions on the page explain some fancy ways to change the values for text and background colors. These are fun and time saving, but the real value in the tool comes from the clear and obvious way it reports on how the colors test out against WCAG 2.0 standards.