SOLDERMASK

The layer on top of the copper foil is called the soldermask layer. This layer gives the PCB its green color. It is overlaid onto the copper layer to insulate the copper traces from accidental contact with other metal, solder, or conductive bits. This layer helps the user to solder to the correct places and prevent solder jumpers.

In the example below, the green solder mask is applied to the majority of the PCB, covering up the small traces but leaving the silver rings and SMD pads exposed so they can be soldered to.

Soldermask is most commonly green in color but nearly any color is possible.