`label.py` does not allow `color=None`

[kmatch98]

When using label.py to create transparent text with color=None the following error is received:

  File "/lib/adafruit_display_text/label.py", line 105, in __init__
TypeError: color buffer must be a buffer, tuple, list, or int

Here is my input code:

from adafruit_display_text import label
...
text_area = label.Label(terminalio.FONT, text="Hello world", color=None)

The only time I envision that a Label’s color might be desired to be set to None is when using the builtinFont where the background is done the “old way” that saves memory on the Clue.

In bitmap_label.py we currently accommodate transparent text.

Main question: Should we accommodate transparent text color with label.py? There are two cases where this might be used:

1. Using transparent text as a way of hiding it.
2. Using BuiltinFont with the “old way” of creating the background color and using transparent text.

[kmatch98]

I don't think there are many use cases where label.py would be used with transparent text, so I'm closing this as a non-issue.