Revert "Add colors to faces that lack them."

Revert "Add colors to faces that lack them."

This reverts commit 16748a5f6bd57ec0967ecb5e14ffe8af5f43d888.

From the discussion on the ding mailing list, I said:

I think the colours should be reverted back to what they were before the
change.  Normal text should be white on black (if you have a dark
background), and colours should be used to emphasise or de-emphasise
certain text.  Following that principle, normal Gnus groups should be
white, not ... er...  what are they now?  Teal?