You can use a script like the follwing as the first field's custom validate script:
// Gray "Text2" background if this field is blank, and white if not getField("Text2").fillColor = event.value ? color.white : color.gray;
For more information, see: http://livedocs.adobe.com/acrobat_sdk/9.1/Acrobat9_1_HTMLHelp/JS_API_AcroJS.88.705.html
Thanks that works.
What is the syntax for no color?
I want it siwthed off when there is a value in the field. I looked in the link and did not find the proper sytnax.
If by "no color" you mean transparent, then it's color.transparent .