Comment 5 for bug 553393

If you look into the gtkrc files for the human-theme themes, you'll find this section:
style "murrine-radiocheck"
{
    text[NORMAL] = @selected_fg_color
    text[PRELIGHT] = @selected_fg_color
    bg[SELECTED] = @selected_bg_color # HACK: override button selection colour
}

At first, I though I solved the problem by commenting out the text[NORMAL] line.
#text[NORMAL] = @selected_fg_color

This did solve the menu drop-down issue. However, I soon discovered it created an issue with regular radio buttons and check boxes. They were now black instead of white by default. The black against the dark brown color that is the default for human-themes caused the check/dot to barely be visible.

Next, I commented out the bg[SELECTED] line.
#bg[SELECTED] = @selected_bg_color # HACK: override button selection colour

This lightened the brown color in the background of checked check boxes and radio dots to a usable state. It works, but it's hardly ideal.

Ideally, I'd expect checks/dots in drop-down menus to be black by default and white when moused over. I'd expect regular check boxes and radio dots to be white normally and black when moused over.