color reversal in one aspect of powerpoint

[Bill Baker]

Poerepoint has been operating OK but now has started to
produce what look like negative colors. All is fine in the
side sorter view and when running a presentation but on
changing from sorter to the edit view the colors change.
Greens become reds, blue-grey of water is purple and the
greyish sky goes light blue. I have checked for viruses
and reloaded powerpoint from my own and other CD's but the
problem remains.