everything that you can "touch" in battlefield is a "physical" object called a mesh... the mesh has shape, but is not visible.
the things that you can see in the game are called textures. they are put around these shapes like skin... hence the name skin. The textures are just pictures.
so everything that you see in the game is a texture, which is givin the nickname "skin"
the skin can be changed to look however you want it to, in this case, coloring the soldiers red and blue by modifying the games texture file.