Plotting question

Hi,

I use R to draw my graphs. I have 100 points on a simple xy-plot. The points are
distinguished by a third variable which is categorical with 10 levels. I have
been plotting x against y and using gray scales to distinguish the level of the
categorical variable for each point. It looks ok to me but a journal reviewer
says this is not any use. I cannot afford to pay for colour prints. Any ideas on
what is the best way to distinguish 10 groups on an xy scatter plot?

If all else fails I can just remove the graph and give them a table of
regression coefficients.


Thanks.

Yours Sincerely
Andrew McCulloch