Yes, REW hides everything; at least as far as I know, there is no color or pattern gene that will overpower that <
cc>. So, you cannot tell anything about any other loci in a REW unless you have a pedigree or do a test breeding.
A broken REW out of your broken black doe would be <
?a ?? cc ?? ?? Enen>.
Since they have a broken dam, chances are decent - 50/50, actually - that one or both of your REWs are genetically broken colored.
To test whether a REW is a broken
En_, breed it to a solid. Chances are very good (though never 100%!) that if it's a broken, you'll get at least one broken kit in the litter, which you will know came from the REW parent.
The same goes for BEW; it's hard to say what's under the genetic whitewash, other than that you can say for sure it's not
cc, as REW trumps BEW.
One of my most successful white Satin does, Diamond Chip, genetically was a broken blue. She produced many broken kits with solid bucks, and only blues/broken blues when bred to self blue bucks:
View attachment 41100
And Jazzy here, our old man BEW Polish buck, is genetically a broken chestnut. He produces solid (well, solid or solid with small vienna marks) and broken chestnuts with our self black does:
View attachment 41099