Cell formatting by formula or macro?

Hi,

I was hoping someone can help me please.

A1=text A2 will either be "yes" or "No"

What I want to do is format A1 by either a fill colour or text colour. Any type of format I guess. If A2 is "Yes" then A1 is green and If A2 is "No" then A1 is red.

Many thanks in advance and probably sorry for being a bit thick.

Mark