Do you want to change the field's border color, background color, or something else? Here's how you can change the border color:
// On Focus script
event.target.strokeColor = color.blue;
// On Blur script
event.target.stroleColor = color.black;
But use whatever colors you want.
Thanks George. That is exactly what I am looking for. If I do want to change the background color, what is the code for that?