You can change the Start menu to any custom color you want, but that will, by default, change the Taskbar to the same color. To do this, open Settings > Personalization > Colors. Select dark mode then ...
I just realized today that some of my pinned websites no longer opened on my Taskbar, so I went to repin them and found I was unable to re-pin them to my Taskbar or Start Menu. I tried doing a repair ...