Leave invert(N) alone; it's a CSS filter. Fixes #331

2 files changed, 11 insertions, 0 deletions

diff --git a/scss/extension/core.py b/scss/extension/core.py
index 7b69315..966a830 100644
--- a/scss/extension/core.py
+++ b/scss/extension/core.py
@@ -378,6 +378,12 @@ def invert(color):
     """Returns the inverse (negative) of a color.  The red, green, and blue
     values are inverted, while the opacity is left alone.
     """
+    if isinstance(color, Number):
+        # invert(n) and invert(n%) are CSS3 filters and should be left
+        # intact
+        return String.unquoted("invert(%s)" % (color.render(),))
+
+    expect_type(color, Color)
     r, g, b, a = color.rgba
     return Color.from_rgb(1 - r, 1 - g, 1 - b, alpha=a)
 
diff --git a/scss/tests/extension/test_core.py b/scss/tests/extension/test_core.py
index 7151c76..4e83e99 100644
--- a/scss/tests/extension/test_core.py
+++ b/scss/tests/extension/test_core.py
@@ -152,6 +152,11 @@ def test_invert():
     assert calc('invert(yellow)') == Color.from_rgb(0., 0., 1.)
 
 
+def test_invert_css_filter():
+    # invert(number) is a CSS filter and should be left alone
+    assert calc('invert(50%)') == String("invert(50%)")
+
+
 # ------------------------------------------------------------------------------
 # Opacity functions