ppmrainbow

Generate a rainbow. More information: https://netpbm.sourceforge.net/doc/ppmrainbow.html.

ppmrainbow color1 color2 ... > path/to/output_file.ppm

ppmrainbow -width width -height height color1 color2 ... > path/to/output_file.ppm

ppmrainbow -norepeat color1 color2 ... > path/to/output_file.ppm