So an idea I had is that maybe wearing blue glasses might increase alertness. I've been weirdly fatigued during the day lately, even though I've been using melatonin and redshift. But does the /absolute/ magnitude of the blue light matter, or the amount of blue relative to other colours? Blue glasses would mostly have no effect on the absolute amount, but would increase the relative amount.

Unless the mechanism which causes our pupils to constrict is itself sensitive exclusively to blue light those blue glasses will increase the absolute amount of blue light that make it into your eyes.