LOL
I got the same problem on my last grow man - there are 2 solutions i found:
1. rotate and move the plant around so lower parts of it were under the blue diodes (ie were further away) its almost invariably the blue diodes (or maybe cool white i guess, cant remember your setup) that are causing the bleaching. maybe you could rotate tina 180 degrees? Dunno how much itll help under your nice even canopy.
2. lower the ambient temperature. Bleaching occurs when energetic blue photons (especially) are turned into heat in the leaves/buds, so lowering ambient temps will lessen its' effect. I actually only began to get bleaching late in flower because we had a seriously warm spell compared to the frigid conditions in early/mid flower.