turns out 'git diff' adds reset to the start and end of context lines

Author: dougthor42

Lib/_colorize.py

@@ -212,6 +212,7 @@ class Difflib(ThemeSection):
     """A 'git diff'-like theme for `difflib.unified_diff`."""
     header: str = ANSIColors.BOLD  # eg "---" and "+++" lines
     hunk: str = ANSIColors.CYAN  # the "@@" lines
+    equal: str = ANSIColors.RESET  # context lines
     insert: str = ANSIColors.GREEN
     delete: str = ANSIColors.RED
     reset: str = ANSIColors.RESET

Lib/difflib.py

@@ -1161,7 +1161,7 @@ def unified_diff(a, b, fromfile='', tofile='', fromfiledate='',
         for tag, i1, i2, j1, j2 in group:
             if tag == 'equal':
                 for line in a[i1:i2]:
-                    yield ' ' + line
+                    yield f'{t.equal} {line}{t.reset}'
                 continue
             if tag in {'replace', 'delete'}:
                 for line in a[i1:i2]:

Lib/test/test_difflib.py

@@ -366,7 +366,7 @@ def test_unified_diff_colored_output(self):
              "\033[36m@@ -1,2 +1,2 @@\033[0m",
              "\033[31m-one\033[0m",
              "\033[32m+two\033[0m",
-             " three",
+             "\033[0m three\033[0m",
         ]
         self.assertEqual(expect, actual)