Geant4 User's Guide for Application Developers - Geant4 - CERN

Visualization8.6.2. Colour8.6.2.1. ConstructionClass G4Colour (an equivalent class name, G4Color, is also available) has 4 fields, which represent the RGBA(red, green, blue, and alpha) components of colour. Each component takes a value between 0 and 1. If an irrelevantvalue, i.e., a value less than 0 or greater than 1, is given as an argument of the constructor, such a value isautomatically clipped to 0 or 1. Alpha is opacity, which is not used at present. You can use its default value 1,which means "opaque" in instantiation of G4Colour.A G4Colour object is instantiated by giving red, green, and blue components to its constructor, i.e.,G4Colour::G4Colour ( G4double r = 1.0,G4double g = 1.0,G4double b = 1.0,G4double a = 1.0);// 0