Otherwise, the error is only raised when drawing the artist, which is
always confusing. Also add a general_check_color_like mechanism and
use it for Line2D as well, instead of relying on a slightly strange
if not is_color_like(): check_in_list(get_named_colors_mapping())
call where the check_in_listalways fails.

Closes#19569 (well, likely the OP was confused about other stuff, but this should at least bring the error message closer to the relevant place).

PR Summary

PR Checklist

• Has pytest style unit tests (andpytest passes).
• IsFlake 8 compliant (runflake8 on changed files to check).
• New features are documented, with examples if plot related.
• Documentation is sphinx and numpydoc compliant (the docs shouldbuild without error).
• Conforms to Matplotlib style conventions (installflake8-docstrings and runflake8 --docstring-convention=all).
• New features have an entry indoc/users/next_whats_new/ (follow instructions in README.rst there).
• API changes documented indoc/api/next_api_changes/ (follow instructions in README.rst there).