In Windows 10, icons and start menu tiles are drawn on top of a bounding rectangle of their size that acts as background and is colored using the accent color, whereas in Windows 7 and prior, there was no such background.
In my opinion, displaying nearly every icon/tile with the same color is a bad design choice and does not appeal to me at all.
Is it possible to make the background of icons transparent?
Or at least
change the background color to black (which is not available as accent color) or use an image as background (as in the mobile version)?
Tiles that do have a transparent background should probably have some thin outline, but this seems impossible more than ever.
Update: You can now choose a custom accent color, so setting it to the start menu's background color should give a satisfactory result.