The problem is really hard to describe ...
Start10 1.75 + Curtains 1.15, no mouseover defined, color is taken from accent settings, displayed everywhere after mouseover
Start10 1.96 + Curtains 1.17, mouseover is defined, the color is entered from the image 64x64px, "All programs, Shut down" is not displayed, respectively only the gray color in ALL themes I tried.
Note the first screen in the post that in Curtains, for example, passing a topic to the toolbar does not work even though it is enabled. Start10 has the main word here and skins the taskbar. However, the buttons are taken from the Curtains topic. It's such a mix. At that time, I did not yet know all the details.