This is a good question. I don't know the answer for certain but my three oldest buns, 9,8,&8, have all darkened considerably with age. My one bun used to be a honey color and now is really dark - I was comparing a photo taken of him yesterday with one when he came to me at 6 months and it is amazing. So from my experiences I would say yes, they definately darken with age, well a light bun, my 8 year old dark dwarf is getting lighter lol. I have only had the two since they were already seniors, but my dwarf didn't start getting dark gray patches until he was about 6 years old.