Did I ruin my Mauser bolt? (with pictures)

[Cb750k]

I've had similar color change happen when cleaning motorcycle carb parts in my ultrasonic, cleaning solutions can react with certain metals resulting in discoloration. I wouldn't worry about it but that's just me.

 

[sunray]

There's absolutely no way a light bulb in an oven will ever take the temper out of anything. The oven light by itself won't dry anything either. Set your oven on the lowest temp it has and you'll be fine. No need for the towel.
I suspect you've just coloured the bolt a bit with the brass cleaner. No big deal.
And shut off your caps lock.