Simply change color of MC via FlashVars

I’m setting up a simple Flash file (AS3) & want to check a flashvar on the first frame of my movie. The flashvar would be boolean to switch between two different values. If the flashvar is true the background MC would be purple. If the flashvar is false the background MC would be red.

I’m new to AS3 and mainly just a designer (some familiarity w/ AS2 in the past). Can anyone help me out with this. I’m not sure how exactly this should be constructed via code.

Thx in advance!