Overview background should fade in from/back to black the same as the top bar
Currently in Shell 40 only the top bar fades from black to grey when opening the overview, creating what looks like a graphical glitch, since there's momentarily a hard edge between the top bar and the rest of the overview background, until it's finished fading to grey.
This could be fixed by having the overview background start off black and fade to grey with the top bar, making the animation seamless.