code: func (gt *GLTriangles) Color(i int) pixel.RGBA {
  	r := gt.data[i*gt.vs.Stride()+2]
  	g := gt.data[i*gt.vs.Stride()+3]
  	b := gt.data[i*gt.vs.Stride()+4]
  	a := gt.data[i*gt.vs.Stride()+5]
  	return pixel.RGBA{
  		R: float64(r),
  		G: float64(g),
  		B: float64(b),
  		A: float64(a),
  	}
  }
docs: // Color returns the Color property of the i-th vertex.