color bugfix + more work on theme generation function

rio/color.py

@@ -508,7 +508,7 @@ class Color(SelfSerializing):
             darken the color instead.
         """
         # The amount may be negative. If that is the case, delegate to `darker`
-        if amount <= 0:
+        if amount < 0:
             return self.darker(-amount)
 
         # HSV has an explicit value for brightness, so convert to HSV and bump
@@ -550,7 +550,7 @@ class Color(SelfSerializing):
             the color instead.
         """
         # The value may be negative. If that is the case, delegate to `brighter`
-        if amount <= 0:
+        if amount < 0:
             return self.brighter(-amount)
 
         return Color._map_rgb(self, lambda x: max(x - amount, 0))

rio/theme.py

@@ -809,7 +809,6 @@ def _create_new_theme(
     """
     Experimental next-gen theme creation function.
     """
-
     # Accent palette
     if accent_color is None:
         accent_color = rio.Color.from_rgb(red=0.3, green=0.55, blue=0.92)
@@ -898,7 +897,11 @@ def _create_new_theme(
 
     # Keep the disabled palette subdued. It's not meant to be perfectly
     # readable
-    disabled_color = rio.Color.from_grey(0.6)
+    disabled_color = _derive_color(
+        neutral_color.desaturated(0.8),
+        0.15,
+        bias_to_bright=-0.3,
+    )
 
     disabled_palette = Palette(
         background=disabled_color,