The color is absolutely fine....I don't use d2 much but I use a lot of stainless and occasionally some carbon but not much from what I know d2 is kinda semi stainless....I put a lil piece of balled up paper in the foil UNLESS IT IS DAMASCUS!!! if its Damascus especially stainless Damascus it can effect the etch and the pattern if you put ANY THING in the foil wih the steel. Anyway I always get some lil bit of coloration on it when it comes out no big never cause a problem...I have come to think the only way to prevent that is to run something like argon into the oven to push out the oxygen but that has its wn problems you would want to do that inside in a very in ventilated room. if you want to go that route I think ray has his oven set up like that. but really the color-ing is no big deal so I wouldn't worry
This is crucibles spec sheet for d2 take a look it will show how to hrden and also what tempering temps provide what hardness levels....keep in mind its a sarting point I always start with the spec sheet and improve from there.
http://www.crucible.com/PDFs/DataShe...dsD2v12010.pdf