Basic rules of web design - Consistenet layout

Your web page layout and design should be consistent throughout the site

Just as in any document formatted on a word processor or as in any brochure, newsletter, or newspaper formatted in a desktop publishing program, all graphic images and elements, typefaces, headings, and footers should remain consistent throughout your web site. Consistency and coherence in any document, whether it be a report or a set of web pages, project a professional image.

For example, if you use a drop shadow as a special effect in your bullet points, you should use drop shadows in all of your bullets. Link-colors should be consistent throughout your web pages. Typefaces and background colors, too, should remain the same throughout your site.

Color-coded web pages, in particular, need this consistency. Typefaces, alignment in the main text and the headings, background effects, and the special effects on graphics should remain the same. Only the colors should change.
source: http://www.grantasticdesigns.com/5rules.html