[ANN] mode named colors

Hello,

I just uploaded a new version of my Color package on SqueakMap:
http://map.squeak.org/account/package/4fcb1d4d-ff16-46e2-bfa8-a7410f0cd5a3/autoversion/6

I fixed the color display list so that it scrolls smoothly. In the
process, I noticed that the attached change makes the BitBlt color cache
computing twice faster, simply by avoiding operations on fractions.

I think this should be in the trunk.

Stef