Hi @dayet .
The colors in your materials do not get exported as they are set through the “Subsurface Color” socket in your shader nodes, which we don’t treat when processing Blender files (the way we handle subsurface is different than in Blender, so we don’t try to convert this info from Blender and take the risk to have “broken” results).
By the way, the issue is the same for the gradient colors you use on some parts of the shoe: as we don’t support those kind of nodes in Sketchfab, the info does not get translated between Blender and Sketchfab.
In order to get the colors of your materials exported to Sketchfab, I would recommend two approaches, which should give you satisfying results (with a general recommandation towards the first one, baking the colors into the textures):
Modify the image textures in your favorite texture editor to bake the color into it.
In GIMP for instance, I would create one layer with the original texture, one layer with the color I want, and merge the two together. This way, the patterns of the BW texture as well as the color in itself will “live” in the same image, which will make it easier for our viewer to handle your data.
Note that a similar approach would be the only way to transfer your gradient texture into Sketchfab, but for this you will need to bake the texture nodes into an image. CF this doc on Blender or this video for instance if you are not too familiar with texture baking.
Use vertex colors.
This method can be a little more complex to setup, and I would not advise it for your workflow, but our viewer multiplies the basecolor of Sketchfab materials with the vertex colors of the object, if they are detected.
-> A plain white color with red vertex colors will end up in a red material for instance.
-> A red texture used as base color with white vertex colors will also end up in a red material.
-> A BW texture with vertex colors will darken the color where the texture is black, and keep it as-is where the texture is white.
Hope this GIF from this model can help understand the idea.
Good luck for the challenge !