I've had this little girl for almost a year (I got her in May 2012, and she was a couple of weeks old). She's ghost colored.
She's had that yellowish discoloration for a long time, perhaps even before she came into my home. It's always concerned me, but because she was eating just fine, and displayed all signs of good health, I didn't think much of it.
I recently went on vacation for a week and had my roommate make sure my snake was fine while I was out. When I came back, the yellow discoloration seemed to spread a lot more. It was shocking for me to see it run down much further than it did before I left.
I fed my snake before I left, gave her fresh water, and told my roommate to constantly make sure her cage was clean and the water fresh while I was out. I also had them clean up her waste when she eventually passed it.
This little girl lives in a ten gallon glass aquarium (I plan on moving her to a larger one once she gets big enough), and uses paper towels as substrate. Sometimes I use newspaper.
Her water is changed every other day, and the under tank heating pad stays at a comfortable 80 degrees, give or day several degrees, and it's on one side of the tank. The other is left cool.
I feed her thawed frozen mice (I put them in warm water so they're warm when I feed them to my snake) once a week. Right now, she's eating fuzzies.
I have a feeling this is normal, and just part of her coloring since she never acts strangely. She's active, constantly surveys her environment, eats just fine, and poops fine. Still, I'd rather be safe than sorry.
Any ideas as to what this yellow discoloration is? It goes a little further down than in the picture.