rgbformulae

     set palette rgbformulae <function 1>, <function 2>, <function 3>

Despite its name, this option applies to all color spaces. You must specify one of 36 preset mapping functions by number for each color component. The available functions are listed by show palette rgbformulae. The default is set palette rgbformulae 7,5,15. In RGB space this uses function 7 to map the red component, function 5 to map the green component, and function 15 to map the blue component. A negative function number inverts the sense of that component by mapping f(1-gray) rather than f(gray).

Some nice schemes in RGB color space

   7,5,15   ... default (black-blue-red-yellow)
   3,11,6   ... green-red-violet
   23,28,3  ... ocean (green-blue-white)
   21,22,23 ... hot (black-red-yellow-white)
   30,31,32 ... black-blue-violet-yellow-white
   33,13,10 ... rainbow (blue-green-yellow-red)
   34,35,36 ... AFM hot (black-red-yellow-white)

A full color palette in HSV color space

   3,2,2    ... red-yellow-green-cyan-blue-magenta-red