hello:
I am trying to use R to draw a  3D picture, then color the picture according to the value of z , how could I do this job?
this is my exalple 

x<-y<-seq(-50,50,2)
m<-function(x,y) x^3+y^3-x^2*y-x*y^2
z<-outer(x,y,m)
persp(x,y,z,theta=-60,phi=30)

I want to draw the Zmax in red and Zmin in blue, the value between Zmax and Zmin is colored gradually

thank you very much
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