When you change your background color, be sure to set text colors for the A:link section at the top of the page. This sets the colors for clickable links on the page... if not, clickable links on the Pages: and the navigation bar will be very hard to read.

Also, you should set a default "color:" in the BODY area at the top. This is the default color for any text on the page that is not set anywhere else.

Bottom line: if the Navigation bar or Pages: section at the bottom of your blog are not visible or hard to read (you will only have a Pages: section if you have mroe than 5 posts), then you need to set "color:" in the BODY area at the top, and set your A:link colors near the top of the page to something opposite of your background color. If your background color is dark, use a lighter color and vice versa.