Walther,
I'd have a look at the maximum resolution the combination of the video card
and screen would have without flickering. I'd only suggest using the color
screen if it does 800*600 without flickering. If this is not too small for
your tastes at a 14"....
Personally I'd prefer the mono-screen as I always have quite a few windows
open. If you only run one program at a time or rarely switch maybe the
color 'surplus' is worth trading in  the smaller size. If you want to
develop programs you will always have to check the colors. I used a
14" mono screen (worst of both worlds) and was surprised how the colors looked
I choose on a color screen.