My plate of homemade beauty has to be a white plate?

I'm doing a beauty dish loosely based off of this tutorial: Does http://www.imageguy.com/make-your-own-beauty-dish/ I use the cup must be white or fails to make a difference? How about a cup of silver or something? [Aluminum]

Yes definitely told me White White

[affmage source="ebay" results="90"]White Bowl[/affmage]