There's currently no way to adjust the colours, but I believe this might be coming for 3.14.

As you've noted, you can use PYTHON_COLORS=0 to disable the colours, or you can use NO_COLOR=1 or TERM=dumb. These are documented at:

https://docs.python.org/3/using/cmdline.html#controlling-color

To me, the cmd.exe traceback output on a real screen, not the photo, is readable enough. For background, I prefer the dark blue preset (0,0,128) to black, because the white/black contrast is overly intense. What do you have a problem with?

Personally, I have an issue with the dim purple on black. As did an entire class of students, so not just my eyes and/or monitor.

Same here, unreadable even with default settings, and forcing people to change the terminal settings just to make Python REPL readable is not a viable option. That makes whole feature useless.
Also, why would there be an "OS-windows" tag here? I don't see any configuration for linux either.

@evle-zzz, the OS-Windows tag is probably because I posted screen captures for MS-Windows and had not been able to test on Linux at the time. Can you post some pictures from Linux?

It would be nice if PYTHON_COLORS worked along similar lines to LS_COLORS, but with a better syntax, perhaps allowing either individual settings or a theme name.

[Note to self and anyone else thinking of contributing code, this links to the original submission]

This is an accessibility issue. Regardless of personal preference, readability, or operating system, these colors should really be customizable to accommodate color blindness.

For a hacky workaround, put a usercustomize.py in your pythonpath with something like:

import _colorize
_colorize.ANSIColors.MAGENTA = '\x1b[0;38;5;13m'
# ...other changes...

Two details about usercustomize.py:

1. pythonpath is found via import sys; sys.path and can be expanded using the env var PYTHONPATH
2. In a virtual environment, ENABLE_USER_SITE might be False unless you also (in the case of the venv module) use --system-site-packages. You can see how this variable is set using python -m site

The color class is listed below. Traceback uses both magentas and both reds.

class ANSIColors:
    BACKGROUND_YELLOW = "\x1b[43m"
    BOLD_GREEN = "\x1b[1;32m"
    BOLD_MAGENTA = "\x1b[1;35m"
    BOLD_RED = "\x1b[1;31m"
    BLACK = "\x1b[30m"
    GREEN = "\x1b[32m"
    GREY = "\x1b[90m"
    MAGENTA = "\x1b[35m"
    RED = "\x1b[31m"
    RESET = "\x1b[0m"
    YELLOW = "\x1b[33m"

Many terminals support at least 256 color ANSI escape codes, and the true color format is ESC[38;2;<r>;<g>;<b>m (decimal digits; not hex)

Until someone implements a theme system for Python, here is a workaround: unfuck_python_colors.py. You may run it in any virtualenv to create a sitecustomize.py file there that hacks these colors to be reasonable.