Dont use neighboring tab colors for tab bar margins on translucent OS windows

The colors are rendered semi-transparent which effectively means they blend
with background unlike the neighboring colors and end up not matching

docs/changelog.rst

@@ -186,6 +186,8 @@ Detailed list of changes
 
 - macOS: Fix using Fn key for start dictation not working (:iss:`9661`)
 
+- Don't use neighboring tab colors for tab bar margins in translucent windows (:iss:`9663`)
+
 0.46.0 [2026-03-11]
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 

kitty/options/definition.py

@@ -1795,7 +1795,9 @@ opt('tab_bar_margin_color', 'none',
     long_text='''
 Color for the tab bar margin area. Defaults to using the terminal background
 color for margins above and below the tab bar. For side margins the default
-color is chosen to match the background color of the neighboring tab.
+color is chosen to match the background color of the neighboring tab, unless
+the window is translucent, in which case the default background is used as it
+looks better.
 ''')
 
 opt(

kitty/tab_bar.py

@@ -19,6 +19,7 @@ from .fast_data_types import (
     Color,
     Region,
     Screen,
+    background_opacity_of,
     cell_size_for_window,
     get_boss,
     get_options,
@@ -695,7 +696,8 @@ class TabBar:
                     blank_rects.append(Border(0, tab_bar.bottom, vw, central.top, bg))
         g = self.window_geometry
         left_bg = right_bg = bg
-        if opts.tab_bar_margin_color is None and opts.tab_bar_margin_width > 0:
+        if opts.tab_bar_margin_color is None and (
+                opacity := background_opacity_of(self.os_window_id)) is not None and opacity >= 1:
             left_bg = BorderColor.tab_bar_left_edge_color
             right_bg = BorderColor.tab_bar_right_edge_color
         if g.left > 0: