Dr Smurto answered it in this post on the previous page.
EDIT - + 1 for the DO instrument testing and mutation observations on the yeast themselves would be the next step.
From everything I've seen, adding H2O2 and methylene blue will actually remove the blue colour. Over the hour or so I thought the blue in the 'saturated' solution was becoming less, but I couldn't be sure.
This morning the 'saturated' solution was as pale yellow as the ascorbic acid reduced solution. Other solutions were unchanged overnight. These other solutions had 0.001% H2O2 in them, vs the 4mL of 12% I had in 40mL of solution to make up the 'saturated' standard.
The studies I've seen use metal catalysts to speed up the reduction, while it still took 6-12hrs with no catalyst.
This doesn't exactly prove that there are not other oxidation products making the MB go blue. There is a 2H2O2 > 2H2O + O2 decomposition that will occur in water, which is significantly sped up in the presence of yeast - so I'm hoping this produced oxygen to show blue, rather than something else.
I'll have to get my hands on a DO meter from Tech Rentals next time...