Soldermask is functionally the "mask layer" that defines the size and location of all of the solderable surfaces of a PCB. This layer protects much of the copper surface of the PCB from oxidation and allows the other conductors of the outer layers to remain isolated during assembly processes. 

Green soldermask has long been the industry standard color. This holds true for Sunstone's ValueProto product as well. 

Sunstone offers a variety of additional soldermask colors (blue, black, red, white, yellow, orange and purple) through PCBExpress, PCBpro and Custom Quote to allow further customization to your PCB. Proud of your alma matter?  Customize your PCB with your school colors. 

See soldermask capabilities for the minimum dam widths, clearances and registration tolerances.