The command ribcolor sets ribbon color. Even if only particular atoms are specified, the ribbon segment(s) corresponding to the entire residue(s) containing the atoms will be affected. Using ~ribcolor sets the ribbon color to none (no color assigned).
Color_name is a built-in name or a name defined previously with colordef. A special color name is colorpanel, which refers to the color currently defined in the Color Editor.
Color sets per-atom colors and modelcolor sets colors at the model (or submodel) level; surfcolor sets which level is used as the source for visible surface colors. Rainbow sets both per-atom colors and per-residue ribbon colors according to a rainbow gradient across each chain.
See also: color, modelcolor, rainbow, surfcolor, the Actions menu