code: public ColorPixel add(double r, double g, double b){
  		return setRGB_fromDouble_preserveAlpha(r+r_asDouble(), g+g_asDouble(), b+b_asDouble());
  	}
docs: Adds the specified RGB channel values to this pixels RGB channels (vector addition).
  Alpha is preserved.
  @param r to be added to this r
  @param g to be added to this g
  @param b to be added to this b
  @return this pixel for chaining