Why consoles/terminals usually have a black background?

1. Why do traders use black background?
2. What is terminal color?

Why do traders use black background?

The black background is easier on the eye, and could reduce some strain, and make it easier to focus and concentrate on the markets.

What is terminal color?

Terminal colors and ANSI escape sequences

Although most terminal emulators support at least 256 colors, most utilities use one of the main sixteen colors (black, red, green, yellow, blue, magenta, cyan, white, and a high intensity or bright version of each).