Is your FBX model uploaded to Mixamo and modeled in Blender orange colored?
This happened to me because I had a temporary Diffuse color setup. You have to reset the Base color inside Principled BSDF or whichever node you are using.
Step 1) Unlink the connection between Color and Base Color.
Step 2) Reset Base color to white/default value.
Step 3) Re-connect Texture Image Color to Principled BSDF Color.
Step 4) Re-upload FBX to Mixamo and the texture should be proper.
