I just got back from vacation sorry for the delay. If you
> haven't worked out your own solution yet, I took John's
> suggestions and made some very minor additions to them. If
> you are interested, I can post the resulting code which
> allows you to specify a base colormap and then override
> arbitrary sentinels with specified colors.
> One problem with John's algorithm as written in his
> original post, was that the sentinel was included in the
> normalization and should not be.
I think this would make a nice wiki entry if you get the time.