My file is in .obj format: how can I make colours and textures appear?
For this particular format, you must attach, along with the .obj model, the indexation file for colours and textures (..mtl), the texture files (image formats .jpg, .png, .gif or others) and include them together in a zip archive.
It's this .zip that you have to upload to the website.
So .zip = .obj + .mtl + .jpg (or other picture formats). The files should not be larger than 50 MB.