Creating Custom menu Links and Custom Pages

Hi,

I am creating a custom there and need help on two aspects:

I need to make a site which is divided into three categories. So, my questions are:

1. How to create menu with three distinctive links? I mean One link in menu with red background, one with blue and one with green? I read a tutorial which said I need to give separate colors to li-x{} where x is number. But where can I find the number? Any tutorial on this is greatly appreciated.
2. Each link should have separate pages. How to create custom pages such that articles belonging to that category comes under that link? also the theme of each page should reflect the link color (red, blue and green).

Thanks,
Praveen