Use 4 bit color by default on Windows.

This fixes a bug when true color is not supported. Even when vt100
escape sequences are supported, we don't know whether we can actually
use true color.

1 files changed, 8 insertions, 0 deletions

diff --git a/prompt_toolkit/output/color_depth.py b/prompt_toolkit/output/color_depth.py
index 7f58597c..60db04bf 100644
--- a/prompt_toolkit/output/color_depth.py
+++ b/prompt_toolkit/output/color_depth.py
@@ -1,4 +1,5 @@
 from __future__ import unicode_literals
+from prompt_toolkit.utils import is_windows
 import os
 
 __all__ = [
@@ -38,6 +39,13 @@ class ColorDepth(object):
         if term in ('linux', 'eterm-color'):
             return cls.DEPTH_4_BIT
 
+        # For now, always use 4 bit color on Windows 10 by default, even when
+        # vt100 escape sequences with ENABLE_VIRTUAL_TERMINAL_PROCESSING are
+        # supported. We don't have a reliable way yet to know whether our
+        # console supports true color or only 4-bit.
+        if is_windows() and 'PROMPT_TOOLKIT_COLOR_DEPTH' not in os.environ:
+            return cls.DEPTH_4_BIT
+
         # Check the `PROMPT_TOOLKIT_COLOR_DEPTH` environment variable.
         if os.environ.get('PROMPT_TOOLKIT_COLOR_DEPTH') in cls._ALL:
             return os.environ['PROMPT_TOOLKIT_COLOR_DEPTH']