Exporting model and textures from Blender

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I know this is an old question but I see no answers yet.

This might be about enabling the texture when you export .dae file. I have exported AR-tag which I used a simple square plate and the AR-tag image as a texture. It is much more simplistic than your model but I guess the process is the same and I am able to see the texture in Gazebo. This tutorial might help.

When you export as a collada (dae) file from Blender, you should see an option on the left to import textures as well, it's quite easy to miss it.

C:\fakepath\Screenshot from 2019-08-14 15-12-22.png

Is there perhaps a reference in your DAE file to some JPG file? Is this JPG file present in the model folder under the file structure materials/textures/?

The structure of a model folder for models with mesh geometry given by DAE file should be

.
├── materials
│   └── textures
│       └── model_name.jpg
├── meshes
│   └── model_name.dae
├── model.config
└── model.sdf