Usually, the 3D data in stl/obj/asc formats are the most commonly used 3D data formats. The stl format has no color texture, and the obj format has color textures. When you save an obj file, 3 files will be saved together: obj, mtl, and png. Without mtl and png, obj is equal to stl, with no color tuxture. The mtl file is like a bridge, it combines the obj and png.