Just to further confuse things, I have chins born black that fade to pale fairly quickly:
This guy was born jet black with white agouti inner ears. By two weeks, he is showing the agouti banding:
Final color:
Except for the dark lacing on the ears, you would never ever pick black chinchilla for this rabbit, would you?
Wow, that's quite a transformation! Even given the effect of wool sort of stretching color out and making it look paler, that's striking.
All of my chins (both Satin and Mini Rex) start out looking black w/agouti markings - they're indistinguishable from castors or silver martins - and develop the color as they grow.
There is chinchilla and harlequin on the pedigree. But there has to be chocolate since the sister to this Dam is chocolate otter.
Interesting... so there is at least some possibility that the paler one is lilac since both of her dam's parents carried chocolate. There's no guarantee that the dam actually got a copy of the chocolate gene since neither of their parents were chocolate or lilac themselves.
Yes! Exactly. I thought they were black when they were born. Then they looked brown and now chinchilla. So crazy! They don't even look like the same kits.
That is just wild. I know how attentive you are or I'd wonder if someone got two different litters mixed up!
Some of my chins go through a rusty phase where they could be confused with a poor castor from the top view, but they never look that completely brown. But the additional pictures of the lighter one at a younger stage incline me back in the direction of lilac - it looks really chocolatey in these pics.
Weird color changes always make me think of the influence of the sable gene, but I don't really see any other evidence like the shading that usually shows up by this age.
2 more photos for comparison of the 2.
The lighter one does look like it has chocolatey ear lacing now, in this photo.
Bigger issue though is complete lack of ring color. Even though in my experience rings do take a while to show up, I'm now wondering about ermine, a non-extension chinchilla (to be honest that was actually the first thing I thought when I saw your original photos). I always look for the first evidence of ring pattern on the lower flanks/hindquarters. Can you check that out on your mystery bunnies? While you're at it, can you give us a photo comparison with the castor kit?
Some ermines look like pure white rabbits with dark eyes, but others can have very extensive frosting. The newly-recognized Czech Frosty is like that; it's a non-extension chinchilla. It looks a lot like your kits and it is a dense-color chin, not a dilute:
So maybe you have a regular ermine and a dilute ermine...?