It is a common misconception that Gouraud shading is any interpolation of colors between vertices, including for example perspective correct interpolation; the original paper makes it clear Gouraud shading is linear interpolation of color between vertices, specifically.[1] By default most modern GPUs use perspective correct interpolation between vertices which produces a different result than Gouraud shading. The differences will be especially pronounced on polygons stretching deep into the view where the differences between linear interpolation and perspective correct interpolation will be more pronounced.