Rew has black, light grey (chinchilla), black and sandy (chestnut) along with white.
So, even though your REW has chin in his background, he cannot actually carry chinchilla since REW is <cc>, which eliminates the possibility for the chin allele <cchd>. He can still carry either or both of the agouti <A> and self <a> alleles, as well as anything else at any locus other than the C series. (If he did actually produce a smoke pearl, he is <A_>.)
I am intrigued to see their babies. I expected blacks, but instead we got rews and these lovely mystery (to me) colored kits.
I agree with
@RabbitsOfTheCreek, with the suggestion of shading on its feet and ears, it looks like it's possibly a smoke pearl, which is a dilute sable agouti <A_B_cchl_ddE_> That would mean both parents carry the dilute allele <d>, with the agouti <A> coming from the sire (since the dam is a sable, which is a self) and the sable <cchl> coming from the dam.
The repeat breeding of the Californian marked rabbit with the gold tipped steel NZ buck was easier to figure out, I think. The REW/Himi is expected, as well as some steel, but these are lighter grey than last litter.
Those "light gray" kits look like what sables start out looking like. The development of the siamese sable coloration is pretty amazing, as they go through some really dramatic changes.
Here is a newborn sable kit, looking like a pale blue next to its himi sibling:
Here is the sable at 5 days - now it looks like a frosty/satiny blue (this was not a satin-coated kit):
This is a sable (broken, obviously) at about 1 week when blue is becoming more brownish:
Sables at 2 weeks still have the frosty look but are now chocolate-hued rather than blue:
Sable near weaning (around 5 weeks)
And in full color development at around 4- months (adult coat still coming in on back):
