If you have paid close attention to the Linux terminal window, or the windows console, you might notice that the text only comes in a limited set of colors. Why do the colors look like this? The way IBM chose to render text color on the original PC set the standard for text color to follow.
The original IBM personal computer from 1981 used a monochrome screen, where all text was green on a plain black background. Shortly after, IBM introduced the Color Graphics Adapter, the CGA, who was the first to admit color. In those early days of PC history, memory was limited, so IBM squeezed most of the functions out of that limited data.
It can display any color by combining different amounts of red light, pure green and blue. This combination of red + verde + blue (about “RGB”) is the basis for all PC colors. Let's start with the simplest case where you can mix equal amounts of red light, green and blue. Representar esta combinación necesita un valor de “has the international standard symbol for a power button on or next to it” O “off” para cada componente de “RGB”. Y recuerde que un “has the international standard symbol for a power button on or next to it” O “off” además se denomina “bit” en la terminología informática: 1 O 0.
In that simpler case, can take care that one bit represents each color: Red, green and blue. If any of the “RGB” bits is 1, then show red light, green or blue at full intensity. This gives eight possible colors:
| 000 Negro | |
| 001 blue | |
| 010 verde | |
| 011 cian | |
| 100 Red | |
| 101 Magenta | |
| 110 Yellow | |
| 111 White |
You can double the number of colors by adding an extra bit, and this is how IBM defined the CGA standard. En lugar de solo tres bits como “RGB”, CGA implementó colores como “iRGB”, donde el primer bit fue la “intensidad”. If the first bit is set to 1, then the PC would display the color in full brightness. If the first bit were set to 0, then it would show the color with a lower brightness.
IBM en realidad implementó un modelo “iRGB” modified. Si el bit de “intensidad” era 0, then any 1 on “RGB” significaba que los colores rojo, green or blue were set to two-thirds brightness. Y si el bit de “intensidad” era 1, then any 1 on “RGB” significaba que el rojo, green or blue was set to full brightness, but any 0 on “RGB” se configuraba en un tercio de brillo. The only exception was 0110, that received a third green glow (“G”), que convirtió el “amarillo de baja intensidad” en un color naranja o marrón.
| 0000 Negro | 1000 shiny black | ||
| 0001 Blue | 1001 bright blue | ||
| 0010 Verde | 1010 Shining green | ||
| 0011 Cian | 1011 Bright cyan | ||
| 0100 Red | 1100 bright red | ||
| 0101 Magenta | 1101 Bright magenta | ||
| 0110 Brown | 1110 Yellow | ||
| 0111 White | 1111 Bright white |
Con este modelo “iRGB”, CGA was able to display sixteen colors: ocho colores de “baja intensidad” y ocho colores de “alta intensidad”. For other technical reasons, la PC solo podía mostrar los ocho colores de “baja intensidad” como colores de fondo. But the text in the foreground could take advantage of the sixteen colors.
Currently, terminal emulators like GNOME Terminal allow you to change the color palette. Depending on the colors you choose, you may see different colors than those shown here, but still limited to sixteen text colors and eight background colors.
