Sometimes you might have colors, materials, or textures applied to your model in your 3D software, but they don't come through correctly on Sketchfab. There are a few common reasons this might happen.
Missing referenced files
If you're using textures, you need to make sure they are uploaded together with your 3D file, or in the case of some formats such as FBX and Blender, actually embedded in the file. Most software that exports FBX files (for example Maya or 3ds Max) will have an option called "Embed media" in the FBX export options. Blender has an option called "External Data → Automatically Pack Into .blend".
If you're using the OBJ format and have materials defined, you should make sure that a .MTL file (along with any textures) are exported from your software and everything is uploaded with the .OBJ file.
You can also try one of our Exporter plugins for your software to ease the process.
Unsupported materials / shaders
A lot of software uses proprietary rendering engines, unique shaders, or other features that are not supported on Sketchfab, and often not supported or exported into standard formats such as FBX. Some common examples of this are Cycles in Blender, KeyShot software, 3rd-party renderer plugins like V-Ray, and "Appearances" in CAD/BIM software like Revit, SolidWorks, and Fusion 360.
These types of materials typically need to be baked into regular textures, or even recreated in other software. Again, you can also try one of our Exporter plugins for your software to ease the process. The 3ds Max plugin, in particular, is capable of automatically baking your materials.
Too Many Materials
In order to upload your model with your materials, you'll want to remove materials or consolidate your total materials and re-upload. For more details, see Materials and Textures.
This is a very common issue with models uploaded from SketchUp. This blog post might be helpful in uploading from SketchUp.