Use set palette functions 4#4Rexpr5#5, 4#4Gexpr5#5, 4#4Bexpr5#5 to define three formulae
for the R(gray), G(gray) and B(gray) mapping. The three formulae may depend
on the variable gray which will take values in [0,1] and should also
produce values in [0,1].
Please note that 4#4Rexpr5#5 might be a formula for the H-value if HSV color
space has been chosen (same for all other formulae and color spaces).
Examples:
To produce a full color palette use:
set palette model HSV functions gray, 1, 1
A nice black to gold palette:
set palette model RGB functions 1.1*gray**0.25, gray**0.75, 0
A gamma-corrected black and white palette
gamma = 2.2
color(gray) = gray**(1./gamma)
set palette model RGB functions color(gray), color(gray), color(gray)