Black is easy to read on white. Black is not easy to read on navy. White is a better choice for text on navy. Be sure to pick colors for your links that contrast and stand out as well, including hover colors if you use a CSS scripting for a mouseover effect. For heavy text pages, I recommend white or very light colors with black text.
Black backgrounds are just too hard on the eyes.
Whatever your color scheme, be sure to keep it throughout the site. Nothing ruins a good site faster than things changing so much the viewer wonders whether or not they are on your site anymore. These include constantly asking people to sign your guestbook, java script pop ups, java scripting errors that lock up browsers, applets, things that follow around the mouse, and disabling functions. Avoid these pitfalls.