The B/C Perma Blue requires pristine metal to provide good results. If you don't get every last bit of oil, dirt, and other contaminants... You won't get a good finish.
Their Cleaner/Degreaser works well, and comes in the two-pack and three-pack "kits".
The Perma Blue, alone, requires you to use your own degreaser (acetone, denatured alcohol, whatever is available).
Most people have a strong opinion about cold bluing, with only two predominant opinions:
1. It sucks, and shouldn't ever be used for anything more than spot touch-ups.
2. It's fine for entire guns.
...But the "it's fine for entire guns" crowd always manage to leave out the qualifying statement of "You have to put in the effort to properly clean and degrease the metal".
I've seen entire rifles finished with the B/C Cold Blue, and they look fantastic. For example: Cornbush has a sporterized Type 99 Arisaka that was refinished with the product, and it has one of the deepest, most lustrous bluing jobs I've ever seen. ...But he spent nearly two days on metal prep, and applied something like 11 coats of Perma Blue.
It doesn't work well for lazy people. But, if you put in the time, and use the right cleaners, it'll result in a very nice finish. (It isn't as durable as a hot blue, but will still last long enough to be worth it.)