Blackest Black

I'm using TCC inside TCMD 29 and noticed that "color white on black" doesn't produce an entirely black background.

I'm using style Windows Dark and noticed that the area above the tabs is blacker than the tab background. It's not much, but clearly visible in a moderately dark room. Is there some way to make the tab area completely black?

This is more of a "that's odd" issue than a showstopper. Just curious.

Thanks - K1EA