There is info online on faking color case hardening, but the real thing is, well, real.
There are a couple outfits in the US that will do color case for a price.
Setting up to do it yourself is a tough row to hoe.
Need a electic furnace, 1200-1800 degrees F capable, Case hardening carbon source (bone meal charcoal is one used) some pots to pack the stuff in, and a quench tank full of water and assorted chemistry, depending on what recipe is used.
CPA arms does a nice tiger striped version, that matches the traditional finish on the better Stevens single shots. There are a couple outfits that do Winchester style as well.
Cheers
Trev