Green PCB Boards
Most PCB board color you may encounter are green, well that is because of the solder mask layer that covers the surface of the PCB. The solder mask is actually a thin polymer layer covering the PCB surface to prevent oxidation and solder bridges.
Traditionally, solder mask is green, and now there are other colors, such as white, blue, red and so on. However, the green PCB board has become conventional, reasons for why green is usually chosen are listed below.
Green color can relax your eyes.
For people working in the PCB assembly and manufacturing industry, a green PCB is a clear choice as they may spend most of their time analyzing and inspecting these boards, sometimes manually too. Green can help ease fatigued eyes.
Green PCB board is the industry standard.
Green has become widely used in the manufacture of printed circuit boards, making it more available and cost-effective than any other options.
Although solder masks are not commonly used for hand-soldered PCBs, they are very effective in modern PCBs that use reflow or solder bath technology.
The solder mask is just like any other layer drawn in a Gerber file. You may want to provide a solder mask on the front and bottom layer as you like. Of course, options like color depend on the facilitations of PCB manufacturer to some extent.