def coerce(other)
      if other.is_a? RGB
        return other, self
      else
        return RGB.new( other, other, other ), self
      end
    end
def coerce(other)
      if other.is_a? RGB
        return other, self
      else
        return RGB.new( other, other, other ), self
      end
    end
Coerce with other object

 @param [RGB] other Other object.

 @return [Array<RGB>] Result of coercion.

 @private