color: type SetDefaultColoring and drop bool states

Also add a test fixture to always disable coloring so that we get
reproducible test behavior. The few tests that want to check color
behavior (e.g. test_color.py) can still reset/change color values as
needed.

Change-Id: I1808139a63e0862c29bf81d7097e885ca8561040
Reviewed-on: https://gerrit-review.googlesource.com/c/git-repo/+/573621
Reviewed-by: Gavin Mak <gavinmak@google.com>
Reviewed-by: Mike Frysinger <vapier@google.com>
Commit-Queue: Nasser Grainawi <nasser.grainawi@oss.qualcomm.com>
Tested-by: Nasser Grainawi <nasser.grainawi@oss.qualcomm.com>

tests/conftest.py

@@ -18,6 +18,7 @@ import pathlib
 
 import pytest
 
+import color
 import platform_utils
 import repo_trace
 
@@ -28,6 +29,16 @@ def disable_repo_trace(tmp_path):
     repo_trace._TRACE_FILE = str(tmp_path / "TRACE_FILE_from_test")
 
 
+@pytest.fixture(autouse=True)
+def restore_default_coloring() -> None:
+    """Force disable color for reproducible test behavior.
+
+    The few tests that cover color behavior can still reset/change the color as
+    needed.
+    """
+    color.SetDefaultColoring("never")
+
+
 # adapted from pytest-home 0.5.1
 def _set_home(monkeypatch, path: pathlib.Path):
     """