Most Web sites look best with a white background and black text.
If choosing different colours, it's important to be sure that the contrast between colours is sufficient that reading is easy.
- Be careful of using similar colours (for example, light and dark blue).
- Avoid background graphics since these are often rather "busy" and distract the eye from text.
- Don't use a black background. If you must use a dark background, choose a fairly dark colour (or dark grey) instead; although this has slightly lower contrast than (for example) white on black, it is easier to read.
Obviously these rules apply to main text. Headings and other display text can be more varied.
If you use particularly striking colours or colours that often indicate warning (for example, yellow on black), even for small areas of text, these may distract attention from the main text. Be careful not to create too many strong, distinctive colour effects that draw the eye in this way.