color system override

Author: willmcgugan

src/textual/app.py

@@ -371,6 +371,7 @@ def __init__(
                 self._filters.append(DimFilter())
 
         self.console = Console(
+            color_system=constants.COLOR_SYSTEM,
             file=_NullFile(),
             markup=True,
             highlight=False,

src/textual/constants.py

@@ -70,3 +70,6 @@ def get_environ_int(name: str, default: int) -> int:
 
 MAX_FPS: Final[int] = get_environ_int("TEXTUAL_FPS", 60)
 """Maximum frames per second for updates."""
+
+COLOR_SYSTEM: Final[str | None] = get_environ("TEXTUAL_COLOR_SYSTEM", None)
+"""Force color system override"""