With the default Windows settings, the Windows 11/10 Start Menu displays ... instead picks up an accent color from the desktop background – Hence, the Start Menu always wears a dark theme.

you can change the Start Menu background color in Windows 11. Instead of showing whiteish or any other default color, you can choose any other color you like. For that, do the following ...

Personally, I prefer the RosePine theme because of its unique look compared to the traditional Windows 11 Start menu. Its neon-like color background is another major plus point of the theme.