How can you tell if your Guinea pig is a Roan or not?

Well, I guess it just depends on how careful you breed your guinea pigs. I know Roans are really popular with Abyssinians. But there are other breeds in the pictures too. :) Here are some pictures: a href="http://www.freewebs.com/blackstonebunnies/100_0609-1.JPG?0.996599171401751" rel="nofollow"http://www.freewebs.com/blackstonebunnie…/a a href="http://www.freewebs.com/blackstonebunnies/100_0902.JPG?0.5795339507672426" rel="nofollow"http://www.freewebs.com/blackstonebunnie…/a a href="http://www.doominous.org/pigs/doomroan040222.jpg" rel="nofollow"http://www.doominous.org/pigs/doomroan04…/a a href="http://home.comcast.net/~hopkinsj6/PIGS/PGraphics/ain.jpg" rel="nofollow"http://home.comcast.net/~hopkinsj6/PIGS/…/a