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Hi, I'm working with hematoxylin right now, or more appropriately, hematein. http://stainsfile.info/StainsFile/dyes/75290.htm
Hematein is a chemical that stains acids purple/blue.  What is called the hematoxylin solution (Hematoxylin powder, Ethylene Glycol, Aluminum sulfate, Sodium Iodate, Hydrochloric acid, and Aluminum ammonium sulfate). 
The aluminum ammonium sulfate and and aluminum sulfate (http://en.wikipedia.org/wiki/Aluminium_sulfate), are used as mordants - something to bind a dye to a substrate. 
I'm only really concerned with the hematoxylin/hematein, however, I listed the other compounds unless anyone recognizes right away that they might catalyze the following reaction.
I add methanol to the solution, and after I've added a significant enough amount, the hematoxylin solution changes color from purple to yellow.  I know that it's possible for hematein to be further oxidized.  My guess is this is what is happening. 
My question is thus, what would a possible mechanism for this reaction be?  I'm not sure how methanol is reduced. 
Secondly, it only happens after I've added a certain amount of methanol.  What is the reason for this, I don't understand why I don't notice that happen right away.  I know that concentrations matter for determining a total yield (LeChateliers principle), but I thought they would happen regardless, even a little bit, no matter the concentration.
Thanks