Not certain, because I’ve not actually played the charcoal game but once.
It took more cannabinoids than I wanted, so I found other ways of getting the pretty blondes the boss was so enamoured with 
Chances are I used the wrong grade & too much. Having In House analytics made that mistake glaringly obvious. They will also guide me if/when that trick needs added to my arsenal.
Back to your darkened oil. Seems to me that 25min at 78C (boiling point of ethanol) might have partially decarbed and significantly darkened your oil…but that doesn’t seem like a perfect fit…
If you’ve tried the same ratio of crude to your “new bleaching clay”, and boiled it for 25min without darkening, then it might well be a pH dependant (residual acid in your AC) interaction between the clay and your crude. Red is usually a sign of oxidation, especially when pretty blondes are involved.