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