I've never seen or heard of this before. I picked up a few rats a couple weeks ago, including this cute dumbo girl with a split cream mask. I thought it was neat that the spot near her nose was darker than the spot further up her head.

Now her mask is dark brown/grey at the nose, and almost completely faded out further up. I don't have a pic from when I first got her, but the mask was very definitely a solid cream color. Even in these two pics taken 3 days apart, you can see a bit of change.




It looks almost like a himalayan marking, just only visible in the mask areas. Do himalayans change color as they mature? This is girl only about 6-7 weeks old right now.