How old is she?
Change in fur color doesn't really sound like anything to get too worked up about, I don't think. Is she maybe just getting old? Or is she a very young rat that's maybe just growing into her adult color?
yeah, i've had black rats that went almost completely chocolate on me when they got older. though spider seems to be going grey instead so go figure. coat coloring changing isn't uncommon at all and doesn't normally pose any problems, well unless you were showing her or something but that'd be about it. i had a young rat who's but turned brown from pitch black about 5-6 months. i thought it was just the sun lighting up her hair as she would bask in it for hours but then she got old and turned brown (mostly) so it could have been that too. in any case don't worry about it, its normal.
Ok if you say so.... It's just that I've owned alot of ratsys with black fur and this is a first for me. lol Is it a lack of vitamins or something? I noticed it a few days ago but dismissed it as a light trick but it caught my attention again last night so I inspected farther and found that her fur was brown at the base of her hood strip. So it IS somewhat "normal" yes...?
It's called 'rusting' and is completely normal. A lot of dark, solid (non-agouti) rats will rust with age. I had a mink girl who rusted in big patches all over her back as she got older. It's genetic. Some rats 'silver' (get white hairs) and some rust. Most breeders try to breed away from that to get more vibrant colors that stay true longer. Either way, calm down and don't worry, it's no big deal.
That sounds like buck grease to me, but I didn't think females got it that much. You may want to give her a bath and look into the protein content of her diet. It also shows up when a rat is having a myco flair up. Is she sneezing?