1. A housing comprising:a substrate comprising a metal area;
a slot defined in the metal area of the substrate and penetrating through the substrate; and
a filling layer received in the slot and comprising an insulating layer and a paint layer on the insulating layer;
wherein the paint layer comprises:
a base paint layer formed on the insulating layer;
a colored paint layer formed on the base paint layer, wherein the colored paint layer is configured to determine the color of the paint layer; and
a top paint layer formed on the colored paint layer, wherein the top layer is configured to protect the colored paint layer.