Ken, I know exactly what you mean, and sorry, I have not yet totally found the answer, however you can
change background colour of windows
using Personalise/Window color & appearance/Advanced appearance settings. Click in window text area and choose your colour (I'm trying a very pale cream)
For the folder background (aaagh white!) I have spent a little time tweaking my grahics card gamma/contrast/brilliance to achieve the best "viewability" without searing eyeballs!
All the best, Chris
P.S. I'll watch with interest cos I think this tweak should be available, as you suggest!