I tried one of the dark themes - great it works.
After a while, wanted to go back to a light theme. Just about everything else changed its theme to reflect that, but the background of the Advanced MATE Menu did not - it stayed dark. Dark grey text on a very dark grey background isn't very readable
The colour of the background stayed regardless of which colour theme I picked.
What seems to work is removing the menu from the panel (typically needing to unlock it from the panel first), picking the theme you'll stick with for a while, then re-adding the Advanced MATE Menu to the panel. It then picks up the current theme's colours etc.