I find the Windows 7 menu quite hard to differentiate. The default background color and highlighted background color are too similar:
Can I change this without changing the actual theme? Or do I need to choose a high-contrast theme?
I went through the detailed Window Color and Appearance (...Icon, IconSpacing, Inactive Title Bar, Inactive Window Border, ...), and it's just not possible with Aero themes (the pretty glassy effects).
However, yes, you are right, a high-contrast theme will change this menu highlight color for you.
There's a software I think you might be interested in:
My colors - Stardock.com