I've got a pair of off-white/eggshell white knit sneakers. Not sure what the upper knit material is. Possibly cotton? I want to try and turn the uppers from off-white to bright white. Y'know - just standard, default white. I'm assuming the knit material is dyed before it's knitted into the upper structure. Would a non chlorine bleach achieve what I'm trying to do? If not, what is the best method for this, apart from painting them, if there is a way at all?