I'm using gltf files because I was told they are the best files to use with Godot, so I got a pack of a bunch of really lovely trees and other things to use in my game. But when I import it, it has all the materials on the side with the base being completely white. I know how to add textures onto things but it seems there is no way to add anything to the model? How would I use these materials then? Is this my fault or the model creator's fault?