It is a feature to dynamically adjust colours to increase contrast. If the value set to max, then the terminal become white and black. It presents at iterm2 and VSCode's embedded xterm.js Copied from iterm2's document: If text is displayed against a similar background color, the minimum contrast setting will move the text color towards black or towards white to ensure some minimum level of visibility. Setting this slider all the way to maximum will make all text black and white. Related links: https://code.visualstudio.com/updates/v1_41#_minimum-contrast-ratio iterm2's setting have this option: https://iterm2.com/documentation-preferences-profiles-colors.html xterm.js list it as an accessibility feature. https://github.com/xtermjs/xterm.js
This blog post describes the usefulness of this feature: https://jvns.ca/blog/2024/10/01/terminal-colours/ If I have time I may try to implement some version of this