Young rabbits do change color quite often.
Siamese sables are usually grey as kits, but eventually their bodies get brighter, leaving only dark spots on the ears, feet and face.
As an example here's Aroma with her baby, who eventually got her markings:
Showing Aroma's markings a bit better:
For older rabbits sunbleaching is usually the cause of color change. Black rabbits turn brown from being out in the sun during summer (just like people:lol: Cept buns actually turn brighter)
My Sasuke is a prime example... In winter (or if he hasn't been out enough) he's a gorgeous silky black rex. If I let him out a lot in the summer he turns golden brown! Which in my opinion is absolutely stunning, its a shame the rabbit show judges don't see it that way:lol:
I'm not sure what could cause white spots... I can't tell properly by that description but your rabbit sounds like a chinchilla or a variety of sorts.
I can't think of any rabbit that naturally develops white spots, but they can get white hairs from being stressed or bitten. Zakura has a tiny white spot in her neck, most likely caused by Sasuke biting her when he got too horny (he's an entire male, she a fixed doe. I let them out together under supervision a couple of times but I don't do that anymore due to humping.)