Highlighting text with color

[Jeffrey Barish <jeff_barish earthlink net>]

I need to highlight some text in a TreeView.  I know how to change the
color, but I am wondering what color to use.  I am thinking that I should
choose a color that is used elsewhere so that the highlighted text does not
clash with the theme, even if the user were to change the theme.  Perhaps
themes define a color to use for highlighting text.  Where would I find
information about the colors that are defined by themes?  How would I get
one of these colors from within my code?
-- 
Jeffrey Barish