Syntax:
test {terminal | palette [rgb|rbg|grb|gbr|brg|bgr]}
test or test terminal creates a display of line and point styles and other useful things appropriate for and supported by the terminal you are just using.
test palette draws graphically profiles R(z),G(z),B(z), where 05#5=z5#5=1, as
calculated by the current color palette. In other words, it is a beautiful
plot you would have to do yourself with the result of show palette palette 256 float.
The optional parameter, a permutation of letters rgb, determines the sequence of
r,g,b profiles drawn one after the other -- try this yourself for set palette
gray. The default sequence is rgb.