I don't know why it is turning purple, but I know it is -14% superfat. So it is lye heavy. I would not use this for a very long time. I would also strongly suggest that you make no smaller than 500 gram batches of soap, as very small weighing errors create big bad impacts on smaller batches.
I am assuming you are using BHT in an effort to avoid rancidity in oils, but I have no idea what effect it would have on soap. I also would not use soybean oil, as you are not adding anything good to the soap with it, and you are raising your risk of DOS.
I would NOT zap test this for a LONG time.
Does this soap zap?!?
I get a -10 SF using PK flakes when I put this into soapcalc. Something doesn't jive.
Use palm oil for the calculator. I got -14% SF.