Playing with the colors and general design of your site could be dangerous, users may get lost if you change too much. Try to keep the same navigation system and menus and respect your site’s general layout.

Sometimes you want to give your site’s categories a different look, this is good to tell users that they are in a different section.

Amazon has a lot of experience giving some of the sections a particular design. For example, they make clear for users that they are in the Spanish books category adding a wrap with the title of the section (in Spanish language).

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Disclaimer: with this kind of article I want to point out usability and interface problems some sites could have. Please do not take this as an attack, take it as a free advice. I would like to make clear that this design problems could happen for many reasons, including lack of time or money.