Wellllll . . . .
You might get reds out of that cross, but they will probably be smutty. A good red in the Mini Rex has chocolate at the B locus, because there is usually a bit of the dark pigment left on the tip of the hair shaft, and chocolate looks close enough to red to not really show. Neither of her parents express non-extension at the E locus (non-extension [e] is what gives you reds and torts, it is recessive to the normal extension [E] that gives you black and castor), so you can't be sure that she has it. If she isn't carrying non-extension, you could breed her to a red from now to kingdom come, and never get a red.
The most likely result from crossing your red buck to this black doe is castor. Good reds and castors have lots of rufous modifiers to give them that deep, rich color. If this doe has a good castor as a parent, she should be able to give rufous to her offspring, so she could produce some nice castors.
You might get reds out of that cross, but they will probably be smutty. A good red in the Mini Rex has chocolate at the B locus, because there is usually a bit of the dark pigment left on the tip of the hair shaft, and chocolate looks close enough to red to not really show. Neither of her parents express non-extension at the E locus (non-extension [e] is what gives you reds and torts, it is recessive to the normal extension [E] that gives you black and castor), so you can't be sure that she has it. If she isn't carrying non-extension, you could breed her to a red from now to kingdom come, and never get a red.
The most likely result from crossing your red buck to this black doe is castor. Good reds and castors have lots of rufous modifiers to give them that deep, rich color. If this doe has a good castor as a parent, she should be able to give rufous to her offspring, so she could produce some nice castors.