Changing File Explorer background color

That option has been taken away by Microsoft in the actual OS: Windows 10.

 The only change you can do is to change "Window Background"-colour in Skin Studio, However NO Textures can be applied anymore in Windows 10.

Optionally, Download or buy a skin that is made for 10 that has the colour & style you like.

Also, you can change the color directly within WindowBlinds if you like.
Open WindowBlinds, click on "Modify Style" text underneath the "Apply style to desktop" button. Page changes.
Click on "Change system colors" button underneath the color tiles. New window pops up with a list of system colors. A couple of options as to which color you change:
1st option- Preferable perhaps, because it will only change the background color of the Explorer windows. This is a relatively new option though, and I don't think it was there yet on WB v10.5, I think it's just on the betas. Scroll down about 10 lines or so to "System Color :ExplorerBackground", click on it, then click on "Change colour..." button.
2nd option- This will change the overall window background color, including probably some applications and various backgrounds within Windows. Scroll down to almost the bottom of the list to "System Colour :Window", click on it, then click on the "Change colour..." button.  It is best to stay away from extremely dark colors for this color because the color tends to be misused sometimes by applications and may result in dark text on a dark background in various places.
If set, 1st option "System Color :ExplorerBackground" will be used for the Explorer windows instead of what is in "System Color :Window".

Or that