While stopping in at Ace Hardware for some home-improvement items, I browsed the spray-paint section (it's become a habit recently).
I found a color that might work for the dome and cheeks of the Fett helmet: Avacado. It's used for touching up those older 70's model kitchen appliances.
I don't think it can be used by itself, but as a good base coat, with several mists of other colors. I'll buy a can tonight and do a couple test sprays. If it works, I'll post pics of what it looks like on MY helmet, along with brand name and color number info.