There are Green Board offered by us which became popular, the word chalkboard appeared. The color change came later when companies sold steel plates coated with green porcelain-based enamel instead of the traditional dark slate. The sold steel plates coated with green porcelain-based enamel instead of the traditional dark slate.  It is a smooth hard panel, usually green for writing on with chalk; a blackboard. The green board trend was in full swing. Teachers had discovered that a different colored paint was a lot more comfortable to stare at all day, because green porcelain paint cut down on glare.