Originally computer user interface images were formed on CRTs. Humans in all probability didn't believe lot all about colour scheme within those days. a phosphor was ordinarily a super dark color, & lit higher brilliantly after the elctron beam hit it. the man eye adjusts to produce this come out to exist as green or even amber in black, based in phosphors applied in a monochrome screen.

RGB screens continued along a similar vein, applying all the beams placed to in to form white.

By using a advent of teletext, research was done into which primary & secondary lightly colors & combinations worked better for this recently medium. (cite...), from either the palette of black, red, green, yellowness, blue, magenta, cyan & white, it turned retired that cyan or even yellowness in black was occasionally uncovered to exist as optimum by line 1 text cases.

A paired colour scheme (black-on-white), was originally introduced in WYSIWYG Word processors, to simulate ink-on-paper.

the select few population cite studies to show that a color scheme with white (light) text in the black (dark) background is easier to scroll through on a screen, because the moo brightness drives less asthenopia. A caveat is that virtually all places on the web are designed for white backgrounds; GIF and PNG images by using the transparancy bit instead of alpha trend lines tend to show higher with choppy outlines, & various more graphic elements develop more problems.