This very simple tip will help you to check whether the colours you have chosen for your web pages have adequate contrast.
Take a screen shot of one of your web pages, and open it up in an image editing program (e.g., Photoshop). Desaturate the image to remove all colour so that you end up with a greyscale image.
Viewing the page as a set of contrasting grey areas makes it much easier to see whether, for example, there is sufficient contrast between the background colour and text. I was reminded of this tip while reading the Techdis article Colour and Contrast Accessibility Issues: for the design of e-learning materials by EA Draffan and Peter Rainger.