The cold blue @ 200 F I mentioned was taken from an Ithaca Service Manual.
They recommended it for restoring the finish on the frames of the Perazzi's they were then importing when color was worn off. These were made of an alloy steel unsuited for case hardening & was apparently similar to the Factory finish.
These were not exactly what one might call a "Cheap Truck Gun". To add some yellows they mentioned another chemical which could be used in conjunction with the cold blue. I don't recall the name off hand, would have to look it up. I tried some but personally I liked just the blue better. Ithaca recommended Numrich 44-40 cold blue. I tried both it & Oxpho & could tell no difference in the final results.

Miller/TN
I Didn't Say Everything I Said, Yogi Berra