Not everyone can see the same colours when visiting a website. I have found a great tool online to help you define your stylesheet according to the results. This is only a small part of a usability testing for your website.You can check the usability of colour on your website at: http://colorfilter.wickline.org/

Colorblind Web Page Filter provides different ‘coverage’ filters to choose from.

This little nifty engine is based on some levels of

• Color vision deficiencies and Anomalous Forms: Protan, Deutan and Tritan.
• Coverage Testing: Monochrome, Black, White, Gray
• Toggle of images: Scripts, Images and CSS

Checking up my site, I found that I haven’t actually provided a foreground colour on some layers, which resulted in not seeing the text when I was disabling the images.

Check it out. You will be surprised at the results.