[RTTY] Color scheme for MMTTY RTTY

[Tim Shoppa]

The default MMTTY in N1MM color scheme is a white background with dark and
Colored (callsigns classified as dupe, new Q, new mult, new double mult)
letters.

I can read dark text on a white background OK but really struggled with the
colored letters on a white background.

I switched the background to pure black and use white and color letters on
that. Very much happier!

Tim N3QE