Terminals have had a black background since monitors first appeared. This makes sense because a monitor bombards you with light and having a black background mi

Terminals have had a black background since monitors first appeared. This makes sense because a monitor bombards you with light and having a black background minimizes the amount of light you're exposed to, and thus fatigue (looking into a monitor is essentially looking into a lamp). I suppose the first window managers later reversed this with white as the default background; perhaps this has to do with the idea of a desktop metaphor where white backgrounds mirror the typical color of paper, who knows. Note that the tradition is not white on black, but gray on black, because the former has too much contrast which gives it a kind of afterglow effect. Monochrome monitors used to support only a single color, such as blue, orange or green. That's why green on black now has (IMHO silly) "retro" connotations.