Take a look at "Conditional Formatting" in XL Help.

In article ,
dustyv wrote:

Is it possible to create a formula to automatically turn a cell a given
colour?
Example: -
If I type the word "Yes" in a cell I would like the cell to turn red
automatically,
If I type the word "No" in a cell I would like the cell to turn green
automatically.
Is this possible?
If yes please recreate a formula to assist me.
Many thanks -=- dustyv