It is virtually impossible to get actual katam and has been for years because of political strife and constraints on exports. Every "katam" I've checked in the last 5-7 years has been deliberately mislabeled indigo. Even at that, it's not really substantially different than indigo--it does not bleach out, it will still go greenish if you bleach it, etc. The process is more or less the same as indigo, which you can see here for brown and black.
I've not experimented with katha as much, but one of my customers has and she was resoundingly disappointed it its texture, application, and dye.
Honestly your best bet is a nontoxic dye like Manic Panic, because then you could at least pull some of it with a standard color remover to bleach.
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