code: func (c RGBA) Sub(d RGBA) RGBA {
  	return RGBA{
  		R: c.R - d.R,
  		G: c.G - d.G,
  		B: c.B - d.B,
  		A: c.A - d.A,
  	}
  }
docs: // Sub subtracts color d from color c component-wise and returns the result (the components
  // are not clamped).