Rubbed back, cold Bluing turns quite a greyish tone. Some like it, others not so much. I quite dislike the smell
that lingers for quite a time. The best cold blue I have found, is Birchwood Casey's cold blue paste in the plastic tube.
Apply it, apply it another two or three times, then flush the surface with cold water as you rub the cold blue off, then
I oil with WD40. That helps kill the smell. Some of the various cold blues smell more than others.