Change Fill Colour when certain numbers entered

Hi,  I would like to be able to have a text fields fill colour change depending on what number is entered, eg;

if 1, 2 or 3 is entered have the fill change to Red,

if 4, 5 or 6 = Yellow, and

if 7, 8, 9 or 10 = Green.

I am looking at entering the script into the Properties Action Tab wit h aTrigger of "Mouse Exit" and Actionof "JavaScript". Would this be best?

Thanks in advance