If one choose a particular color for either the foreground or background text from the drop down list, the color selected should be "sticky" and remain the default color.
For instance, if one selects a background color of yellow highlight text, the background color box should remain yellow until the user picks another color. It is annoying when one selects some text and chooses a background from the drop-down menu, only to have to re-choose the background color from the menu the next time they select text.
If there is a technial reason not to allow this behavior, then how about adding a "highlighter button," and allow the user to pick the default color to be used to highlight text.