Use `set palette functions <Rexpr>, <Gexpr>, <Bexpr>` 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 <Rexpr> 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 XYZ functions gray**0.35, gray**0.5, gray**0.8
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)