A blackboard - an essential attribute of a modern school - appeared in educational institutions at the beginning of the 19th century. Teachers, instead of personally approaching each student, could now explain the subject at once to the whole class, visually showing the information on a large board. Such boards were made from slate or from wood, which was then covered with black paint. The latter option, due to its low cost, has become more widespread.
Later, a growing industry was able to offer schools plastic and metal boards. The latter have become widespread due to their magnetic properties, which turned out to be extremely convenient in everyday use. Initially, such boards were covered with matte black paint - no one thought about changing the color to another. It was assumed that white traces of chalk would be clearly visible on a black background.
However, science does not stand still - by the middle of the 20th century, experts determined that with prolonged work with images, green is the most optimal color for the eyes. School teachers who received a trial batch of dark green boards confirmed that the color is much better at work, especially on bright sunny days, while black boards with white lettering create an image that is too contrasting in the light of the sun.