What other colours are behind the REW besides tort and REW?
I don't know much about genetics/colouring, but I know that if you breed a REW to it's "masked" colour, you can get that colour as well as some REW. You just have to figure out what colour she masks.
For example, my REW buck, Taj is out of a Seal and a Chinchilla and all the other colours in the pedigree are Chinchilla, so he is a masked Chinchilla. If I bred him to a Chin doe, they could produce Chin and REW.
Emily