First, please check the pg. two meshes:
1, “Mask” mesh with a model png texture and the trouser part is transparent.
2, “Trouser” mesh which is painted with red color. it’s supposed to fill the transparent trouser part of the Mask texture.
Please check the Unity3D screenshot below, the bottom one is the orthographic mode preview.
It is something to do with the scaling (position?) of the trousers and the camera angle.
If you use the pointer to move the camera you can see that the trousers and mask are not in the same plane.