# set terminal pngcairo  background "#ffffff" enhanced font "arial,10" fontscale 1.0 size 600, 400 
# set output 'rgb_variable.7.png'
unset key
set view 63, 58, 1, 1.4
set isosamples 40, 40
set xyplane at 0
set xtics  norangelimit
set xtics   ("R=1" 1.00000)
set ytics  norangelimit
set ytics   ("G=1" 1.00000)
set ztics  norangelimit
set ztics   ("0" 0.00000, "B=1" 1.00000)
set title "RGB coloring of pm3d surface" 
set xrange [ 0.0100000 : 1.00000 ] noreverse nowriteback
set yrange [ 0.0100000 : 1.00000 ] noreverse nowriteback
set zrange [ 0.00000 : 1.00000 ] noreverse nowriteback
unset colorbox
rgb(r,g,b) = int(r)*65536 + int(g)*256 + int(b)
xrgb(r,g,b) = (g-b)/255. * cos(30.)
yrgb(r,g,b) = r/255. - (g+b)/255. * sin(30.)
RGB(R,G,B) =  int(255.*R) * 2**16 + int(255.*G) * 2**8  + int(255.*B)
f(x,y) = 0.4 + sin(sqrt(100.*x**2+100.*y**2))        / (1.5*sqrt(100.*x**2+100.*y**2))
GPFUN_rgb = "rgb(r,g,b) = int(r)*65536 + int(g)*256 + int(b)"
GPFUN_xrgb = "xrgb(r,g,b) = (g-b)/255. * cos(30.)"
GPFUN_yrgb = "yrgb(r,g,b) = r/255. - (g+b)/255. * sin(30.)"
GPFUN_RGB = "RGB(R,G,B) =  int(255.*R) * 2**16 + int(255.*G) * 2**8  + int(255.*B)"
GPFUN_f = "f(x,y) = 0.4 + sin(sqrt(100.*x**2+100.*y**2))        / (1.5*sqrt(100.*x**2+100.*y**2))"
splot '++' using 1:2:(f($1,$2)):(RGB($1,$2,f($1,$2)))        with pm3d lc rgb variable