The problem here is that applications can set a background colour, and that as an application you don't know what colours the user defined. For example Angband

The problem here is that applications can set a background colour, and that as an application you don't know what colours the user defined. For example Angband just sets the background colour to black (not sure about Nethack), so if you defined colours that work well on a light background you're still going to have a bad time. Quite a few other terminal programs (especially those using ncurses or other interactive TUI interfaces) tend to set a background colour. There isn't really a good way to deal with this using the default 16 colours other than never setting any background colours, which can be a bit limiting for interactive applications. The best solution is to have application support for this and using 256 or 24 bit "true" colours (256-colour support is pretty much universal, and 24 bit colour support is very wide-spread).