How can I tell the difference?

[3mina]

While I was figuring out the colours in my humongo-litter I thought I had several blue otters. Now that the kits are furred, I've got three 3 opals, 2 blue otters, 2 castors, 1 black, and 2 black otters, not counting the fosters. So my question is, how do you tell the difference between opal and blue otter before they fur out or can you?

 

[Dood]

Otters lack ring pattern on their saddles as they are technically self in that area.

Opal are agouti based and will have 3 or more bands on the follicle

BUT

Rex fur might make it difficult to determine, hopefully a Rex breeder can help in the subtle differences of opal versus blue otter.

 

[3mina]

I can tell easily after they fur out, how about before they fur out?