Don't colour diff headers white, only bold

CHANGES.md

@@ -7,6 +7,8 @@
 - Improve error message for invalid regular expression (#2678)
 - Fix mapping cases that contain as-expressions, like `case {"key": 1 | 2 as password}`
   (#2686)
+- No longer color diff headers white as it's unreadable in light themed terminals
+  (#2691)
 
 ## 21.12b0
 

src/black/output.py

@@ -81,7 +81,7 @@ def color_diff(contents: str) -> str:
     lines = contents.split("\n")
     for i, line in enumerate(lines):
         if line.startswith("+++") or line.startswith("---"):
-            line = "\033[1;37m" + line + "\033[0m"  # bold white, reset
+            line = "\033[1m" + line + "\033[0m"  # bold, reset
         elif line.startswith("@@"):
             line = "\033[36m" + line + "\033[0m"  # cyan, reset
         elif line.startswith("+"):

tests/test_black.py

@@ -200,7 +200,7 @@ def test_piping_diff_with_color(self) -> None:
         )
         actual = result.output
         # Again, the contents are checked in a different test, so only look for colors.
-        self.assertIn("\033[1;37m", actual)
+        self.assertIn("\033[1m", actual)
         self.assertIn("\033[36m", actual)
         self.assertIn("\033[32m", actual)
         self.assertIn("\033[31m", actual)
@@ -323,7 +323,7 @@ def test_expression_diff_with_color(self) -> None:
         actual = result.output
         # We check the contents of the diff in `test_expression_diff`. All
         # we need to check here is that color codes exist in the result.
-        self.assertIn("\033[1;37m", actual)
+        self.assertIn("\033[1m", actual)
         self.assertIn("\033[36m", actual)
         self.assertIn("\033[32m", actual)
         self.assertIn("\033[31m", actual)