If a skin with transparent pixels on the first layer is uploaded, the transparent pixels render as black pixels in-game. In Java Edition, a skin allows only a solid color transparency is not allowed on the skin file except on the second layer, which is transparent by default playing offline, pixels can be left free resulting in 'holes' in the skin. The second layer can be used to give the character glasses, hats, or other accessories (even a bigger head).
Skins with slim arms have 3,136 pixels, with 1568 pixels on each layer. There are a total of 3,264 pixels that can be customized, with 1,632 on each layer. Skins are divided into areas that act as the surface area of the character (for example, the front head area, left leg area, etc.).
