This is the first nut I've ever attempted. When I cut the blank to length, I noticed this discoloration. I thought that since I used a power sander that maybe I'd burned it, but I've seen videos of people using sanders and I don't think I did anything different than them. The blank came from Stew-Mac. Can this be fixed or do I need a new blank? Thanks.
That looks like a bleached nut/bone so the core you're exposing is going to be the proper hue of the bone...
check the following link and you'll see the difference in the first two examples: http://www.stewmac.com/Materials_and_Supplies/Nuts_and_Saddles/
I've seen this happen when I get a little to aggressive when sanding the blank to rough length on my 5" disk sander. Try sanding at a slower feed rate (which heats up the blank less). I finish sand to final length on a block using 220 grit (followed by finer grits) and this usually removes the discolored area. Periodic cleaning of the sanding disk may also help as the sand paper is more efficient when free of built up waste material.
As others have said - this is pat of the charm of working with bone and you often reveal some very neat patterns as you cut, sand an polish a blank. I prefer bone blanks (bleached or not) for a lot of reasons and the character in each piece of material just makes it extra special.
I've always taken that effect as an artifact of the bleaching process. You can imagine that if the bleach had penetrated farther, the color would be white all the way through. It's a bit of a balance - if the bleach its too intense, it can degrade the structure and hardness of the bone.
Perfectly normal and once you get to the final shape and use files and abrasives to polish the nut it will be more uniform and cool looking.
A related topic is using accelerator to glue in a bone nut. Accelerator can discolor the nut slots for a while, it goes away in time, but initially there is some discoloration. I don't like to hand someone their repaired instrument with this discoloration so I've gone to standing there holding the sucker for about a minute instead of using accelerator just to avoid the temporary discoloration.
One last thing. Not saying that this is the case with your bone blank but some bone blanks of inferior processing quality can still have a lot of grease and oils in them and that can look similar to what you are showing as well but I agree that it's likely in this case a tell tale of the bleaching process.
One really, really last thing too: Unbleached bone is said to be about 10% harder than bleached bone. Although either is certainly hard enough I'm a fan on unbleached bone preferring the natural color that can have a nice vintage amber to it.
You guys are treasure-trove of knowledge and I really appreciate you all taking time out to reply. If I'd have know guitar repair was this much fun, I'd have started years ago. Really interesting stuff. Also, I want to thank Frank for the great instruction and pictures on the Nuts! section of Frets.com.