I've done Color Case hardening.
Rough description of classic CC hardening process:
Block the part up so it doesn't warp (you'll see why later).
Pack part in charcoal (wood and bone charcoal, sometimes fish bits and leather scraps are included). Pack part, surrounded by the charcoal, etc. reasonably tight into a steel box.
Heat box to bright red for extended time (The longer the soak, the deeper the increase in carbon at the surface will penetrate--within limits).
Dump (Spill) the whole thing into water (preferably aerated). Sometimes the old timers would run a very thin layer of oil on the surface of the water.
This process is traditionally used for low-carbon parts. The carbon increases to hardenable levels on the surface while leaving the interior soft.
Of course, Infi is already a carbon steel. I suspect the shock of water quench would very likely crack the part a lot of the time--certainly warp it (thus the blocking ahead of time).
If it survived, you'd have to temper infi afterward, which would abate the colors somewhat--probably a lot (depending upon the temp.)
Not saying it can't be done. Just risky to the steel, and of dubious performance benefit compared with the factory HT--but you could try it and see what happens-- If you work out the kinks, maybe you'd have the latest greatest thing!
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