Why does Text have a transparent background, but List and Data Grid have white backgrounds?
I often have the need for List and Data Grids to have transparent backgrounds.
There probably are people out there who do want white backgrounds for List and Data Grid. So the easiest thing would be to give the Background property a transparent-colour option (i.e. one of the colour blocks is transparent). Implement this on all controls that have a Background property. Problem solved (using a pattern found in many apps)!
I do see other people asking for this too (e.g. Data Grid background should be transparent and show no lines when borders are off), but I am suggestion a solution for all controls that have a Background.