Black text on a white ground is the easiest to read.
Set background, text and
links in contrast (most users expect links to be blue).
Match the background to
the tone of any background image to aid anti-aliasing.
The commonest form of
colour blindness is red/green so make sure you have strong contrast in the blue
element and in overall brightness.
Check in all available colour depths, greyscale, monochrome and a cheap LCD
Check usability with your grandparents
Try to keep things as simple and easy to use as possible.