I would like if in
Preferences > Display > Fields > Current Sort Field
we could set a transparency level for the background color.
So I can fast and easy see which column is sorted, but not completely cover my background image.
Anyone else agree?
Preferences / Display / Options / Blend file background colors with background will do that, although it may affect more than just he sort column. Give it a try if you haven't already.
Edit: Or it might be Preferences / Display / Options / Blend row and column background colors (or both).