Excel XP

I'm wanting to know if there is a way to enter a range of numbers (Example
0-10) and have the background be a certain color.

Example: I enter the number 5 in a cell and then the background would turn
blue and if I entered the number 15 in a different cell then the background
would turn yellow.

I know that I can write a macro that if I enter the number 5 and change the
background color to blue that I can manually run it. I just don't know how
to automate the process.

Any help is greatly appreciated.