Blueing is a chemical reaction with metal that seals it to make it more durable and gives it a nice blueish hue, hence the name.
I also thought of blueing some bits but I believe it only works on steel so don't know how it would turn out on the low grade metal most guns are made of.
You can probably buy a bottle of it from gunsmiths to try.
I think you just have to roughly paint it on, let it sit for an amount of time for the reaction to take place and then clean off the residue.
If you try it I'd be interested to know how it goes...