Use only default (white/black), red for bad, green for good. If you need more than that, like vim or whatever, then maybe a 'fullscreen' TUI is better, with a specified background and foreground. For CLI tools, I'm not sure if I prefer more colours.

The CSS to make the terminals look like iTerm was smooth, to the point I read them as screenshots.

I really wish you wouldn't. All the rinky dink colors and animations screw with the CLI output when you don't correctly detect whether the user's running the app interactively.

Keep it plain text. Regular, old, boring output is good.

This is true for the console in dev tools as well.

Problem there is you can’t change css so at the moment the systems color preference changes thing will look bad.

Important considerations for custom formatters.

If the goal here is to pick a fixed set of terminal colors that contrast on both white/light and black/dark backgrounds, it means you're stuck with midtone colors (between light and dark). This is really limiting for color choice, and lowers the maximum contrast you can have for text because you get the best contrast when one color is dark and the other is light.

Ideally, instead of the CLI app switching to "bright green", it would pick a "bright contrasting green". So if the terminal background was dark, it would pick bright green, and for light background it would pick a darker green. There isn't CLI app implementations for this? This is similar to how you'd implement dark mode in a web app.

I'd be interested to see examples, but I can't think of any web app I've seen where dark/light mode was implemented by only changing the background color. It would be really limiting there too.

There's an ever more basic rule: don't just make your text white (ANSI 37m) because you assume the terminal will have a dark background. Even white-on-black (37;40m), while usually readable, can stand out the wrong way if you assume that everyone is using dark mode.

It's 2026, and app developers are solely responsible for not causing eyehurt, even if their users insist on using the Hotdog Stand theme.

Can you work this into an AGENTS.md ? Just so happen to be working on multiple TUI at the moment: text-based modern web browser, VPS rental console, agentic coding wrapper.

Colors, have been a perpetual nightmare.