I am not at all excited about extending the API of to_rgba to add the ability to template the error message in a limited way. That is typically much better done via

try:
    c = to_rgba(...)
except ValueError as e:
    raise ValueError("some custom and more helpful error message with context") from e  # or from None

and we should not be leaking what is really internal details (helpers that existing to reduce the above boiler plate) into the public API.

I am a bit worried that this passed tests as is_color_like has a special cut-out for the 'C2' style colors which can not be evaluated until after we have rcparams fullly setup. We should sort out if we no longer can ever try to do that, if we need to add a test , or be sure if the affected code paths can never be run during start up. The biggest worry here is adding a "fails to import" type bug which the user can not recover from!

Didn't do anything w/ the return type mostly because I wasn't sure if we wanted class objects to retain the original input.

FWIW, both Patch and Collection go ahead and set the color as the rgba value, e.g.

The original color is retained as a private attribute, but I think only used when updating alpha.

Re the try-except loop: it seems to me that that is basically what _check_color_like is doing, neatly packaged so we don’t need to write it out in multiple places.

I am a bit worried that this passed tests as is_color_like has a special cut-out for the 'C2' style colors which can not be evaluated until after we have rcparams fullly setup.

to_rgba also has a carve out:

And trying to pull the carve out of is_color_like broke the tests, so my guess is it's used in the startup stuff.

Re the try-except loop: it seems to me that that is basically what _check_color_like is doing, neatly packaged so we don’t need to write it out in multiple places.

Yup, and I like it and was just unhappy that lists of colors was using to_rgba_array directly, but it's only used in 5 places and the multiple argument functionality is never used. Basically I just want consistency in color validation, also in where colors are validated, because aside from those I think everything else gets validated in draw time, and some of this has to do w/ inconsistencies in supported args like the auto/none thing happening here.

there is also the decorator approach to hide the internal arg (which will also work for all the to_rgba functions) but I'm worried about runtime:

def error_msg_parameter_name(f, c, errname=None):
    try:
        value = f(c)
    except ValueError as e:
        print(dir(e))
        raise ValueError(str(e) +f'{"is not a valid value for " + errname if errname else "."}')
    return value

Can we clarify the status of this one?

I've moved to draft.

That's fine, honestly I'd prefer a more consistent approach to validation, probably as part of the rcParams work.