Colours of models uploaded to Sketchfab washed out

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
d 1.0000
Ns 0.0000

Two examples:
The uncorrected version can be found here
The version I have manually corrected each of the materials in Sketchfab (so they are the same as in Rhino) can be found here.

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!

Hi Bill - no idea… is there any rhyme or reason to the changes? Are they consistent in any quantifiable way? If so, it might be possible to noodle all the values in Rhino prior to exporting and set them back again afterwards, in a script, say… no other ideas…


Thanks Pascal. I did think of that option, but it sounds just as cumbersome! One suggestion that came up on the sketchfab forum is it might be due to the different colorspace. Sketchfab uses sRGB. I was asked what colorspace Rhino operates in, but could not answer as I don’t know. Does Rhino use colorspaces?

Rhino does not have a concept of color spaces. If possible you should look into importing files such that no color correction is done at all.