With SideKick trunk r13830, the new filter box is
painted with the customized colors for textarea. But
it looks odd because the parser drop down above it,
and the sidekick tree below it both painted with
Another problem is it doesn't set the caret color.
Since the default is black and my background color is
very dark, the caret is hardly visible.
I think it is better not to use the costomized colors
for the filter box for now, to match others. Attached
patch does it.