I am having trouble with models exported from Rhino (via OBJ) for upload to Sketchfab. The models upload OK, but the colours are washed out compared to what they are in Rhino, necessitating a manual correction on Sketchfab for each material. For example, a surface with material (plaster) RGB values of 127,187,142 (Hex code #7FBB8E) turns up in Sketchfab with RGB values of 187,222,197 (Hex code #BBDEC5) - i.e. significantly brighter and less saturated. I then have to edit each of the materials in Sketchfab to correct the colours. I have had a look at the RGB values in the .mtl files that go with each .obj file, and they match what is in Rhino (but obviously converted to decimal values - see below). Same thing happens if I export .dae files.
Definition of material from .mtl file:
newmtl Topo surface
Ka 0.0000 0.0000 0.0000
Kd 0.4980 0.7333 0.5569
Ks 1.0000 1.0000 1.0000
Tf 0.0000 0.0000 0.0000
I asked this question on the Sketchfab forum and nobody seems to know the answer, but it likely has something to do with conversion to sRGB values on Sketchfab. And it is not just Rhino - the same thing happens to hand-coded VRML files. Any suggestions welcome, as correcting each material’s colour values on Sketchfab is time consuming!