Respect the NO_COLOR environment variable to disable colour.

CHANGELOG.md

@@ -2,6 +2,10 @@
 
 ## 0.2.4 (unreleased)
 
+- Respect the `NO_COLOR` environment variable and disable colour when it is set
+  and nonempty (when the default `--color=auto` is used).  For more info see:
+  https://no-color.org
+
 ## 0.2.3 (2023-05-22)
 
 - Fix compatibility with nix-2.3 where `nix --extra-experimental-features` isn't

src/nvd

@@ -764,7 +764,9 @@ def main():
     args = parse_args()
     action = args.action
     NIX_BIN_DIR = args.nix_bin_dir or None
-    USE_COLOUR = args.color == "always" or (args.color == "auto" and sys.stdout.isatty())
+    USE_COLOUR = \
+        args.color == "always" \
+        or (args.color == "auto" and sys.stdout.isatty() and not os.getenv('NO_COLOR'))
     del args.action
     del args.nix_bin_dir
     del args.color