Gnuplot Question

[<nic...@vo...>]

Hello,
I have a Gnuplot question that I would like to submit for you. I want to plot a data file
using pm3d and view map. In this data file the two first column are x and y and I will call 
the third and fourth column R1 and R2 (with the relation R1+R2=1). My problem is that I 
want to attribute one different color for each column R1 and R2 and then  splot on view map
(x,y,R1+R2).Well maybe I am not so clear...I give an example: if the first line of my data 
file is x=0,y=0,R1=0.5,R2=0.5 and I attribute yellow to R1 and blue to R2, R1+R2 will be green. 
Is it possible to draw such map ?? I hope I was clear enough...
Thank you for your great 'faq' internet site and that would be really kind of you to help me.
Best regards
Nicolas Dupuis