There is a hierarchy in which color at the model (or submodel) level is overruled by color at the residue level, which is in turn overruled by per-atom color settings.
The command modelcolor assigns color at the model (or submodel) level. If the atom-spec is blank, all open molecule models will be affected; otherwise, the entire model(s) containing atom-spec will be affected. A color change at the model level will not be visible, however, if color assignments at an overriding level (residue or atom) already exist. Modelcolor only acts on molecule-type models. Model-level color can also be changed in the molecule model attributes panel.
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 colors at the atom level, and rescolor sets colors at the residue level; surfcolor sets which level is used as the source for visible surface colors.
See also: color, rescolor, surfcolor, the Actions menu