I'm 100% certain you just set Windows to light mode because doing that turns the taskbar and stuff white and prevents changes from being made to the colors of the taskbar, start menu, and action center.
So literally all you have to do is one of two things:
- If the drop down box in the 'Choose Your Color' thing says 'Custom', then below that there should be a thing that says 'Choose Your Default Windows Mode' and you should select 'Dark' if you have 'Light' so you can change the taskbar color
- If the drop-down box says 'Light', then just click on it and either select 'Dark' (if you want the full Windows 10 Dark Mode with the darker taskbar) or 'Custom' if you wanna customize it (and if you do select custom, then you'll have to do the same thing as in the first 'fix' to switch the taskbar and stuff to dark mode)