Overlay
From UMAWiki
Each slot requires at least one overlay set but usually receives a list of them. Overlays carries all the necessary textures to generate the final material(s) and might have extra information on how they are mapped. The first overlay in the list provides the base textures, and all other overlays included are combined with the first one, in sequence, generating the final atlas.
UMA standard shader requires three textures provided by overlays, one texture for Albedo/Diffuse color, one texture for Normal map, and Metallic/Roughness.
Overlay Asset
