How do I add a banner at the top of a form where the fill lightens as you go left to right?

Hi - I'm creating a form and along the top is a 2 inch wide banner - in Word I inserted the banner and auto filled the color.  But what I'm wanting to do is to have the banner fill color noticeably lighten as it goes left to right.    I'm thinking I need to create the banner *in* Acrobat, though not sure.    In word I can do this, but it 's too subtle  I'm wanting an affect word can't give me.

Thank you in advance for any help!