Although the Web provides a wide set of design choices, it is important that the final page design be easy to read. Below are some guidelines for increasing legibility.
Your fonts should be a minimum of 9 points in size. Smaller fonts are more difficult to read, especially for the more elderly eyes of potential portfolio reviewers.
The contrast in lightness/darkness between the text and the background must be far enough apart so that the text can be easily read. This is one reason black text on white backgrounds are so popular, even on the Web. See Juicy Studios Luminosity Colour Contrast Analyser for an online test of contrast. The best levels are "AAA."
You are not restricted to just black and white, but you want to avoid shades that are too close together. Some "subtle" contrasts can be too subtle for some readers. Note that different colors such as red and green may actually be the same shade (or darkness). In black and white, red and green both become mid-gray.
Another caution is to avoid bright colors together like Christmas red and Christmas green or hot pink and yellow. When bright colors are right next to each other, they can cause an illusion of vibrating edges called "simultaneous contrast" which makes pages harder to read. One tip is to either use either darker or lighter versions of colors or to separate bright colors with a neutral white, gray or white.