I have to note that different color of IHS because of LM diffusion into surfaces will not affect thermal performance in any way and does not need cleaning. So yes, to get that completely off one needs sanding, which will remove info printed on IHS, question is - is it needed to do at all? That surface is hidden all the time, no-one sees it and about the only time looks of it matters - when one is selling that cpu or cooler or wb. I doubt that selling old cpus or cooling hardware can net anyone big enough money to care as much about that.