For emphasis, the color scheme was swapped to bright background with dark text.
Nowadays the two tend to be switched, since most computers today default to white as a background color.
Video is usually reversed by inverting the brightness values of the pixels of the involved region of the display.
When most computer displays were light-on-dark, it was found that users looking back and forth between a white paper and dark screen would experience eyestrain due to their pupils constantly dilating and contracting.
[2] Today, people with visual impairments such as ocular toxocariasis may find it less tiring to the eyes to work with a predominantly black screen, since modern operating systems usually display a lot of white in a normal use.