diff --git a/README.md b/README.md
index 0bc779b..57574ab 100644
--- a/README.md
+++ b/README.md
@@ -217,8 +217,11 @@ with the Secret Key from your Emergency Kit.
   Font License); it is copied to `~/.fonts` at the first start, which is
   how the toolkit makes a font known. Codes and fingerprints use DejaVu
   Sans Mono, which Ubuntu ships.
-- **Light and dark** *(1.1)* follow the desktop where it reports one;
-  *Settings → Appearance* chooses one either way.
+- **Light and dark** *(1.1)* follow the desktop where it reports one
+  (GNOME's colour scheme, or a theme whose name ends in `-dark`), asked
+  **once, at start**: change the desktop while SecretSpace runs and it
+  follows at the next start. *Settings → Appearance* chooses one either
+  way.
 - **A package instead of an installer.** The `.deb` does what the Windows
   installer does: a menu entry, data in your home folder, removal that keeps
   the vaults. Unlike the Windows installer it does not offer to move a vault
diff --git a/sourceFiles/tests/test_look.py b/sourceFiles/tests/test_look.py
index 25037fd..e21b97d 100644
--- a/sourceFiles/tests/test_look.py
+++ b/sourceFiles/tests/test_look.py
@@ -153,6 +153,12 @@ def window():
     root.withdraw()
     yield root
     root.destroy()
+    # Collect what the window left behind here, in the thread Tk lives in.
+    # Fonts and images delete themselves through Tk; collected later from
+    # another thread (a test server's, say) each waits a second for a main
+    # loop that no test runs, and the request being served times out.
+    import gc
+    gc.collect()
 
 
 @pytest.fixture
diff --git a/sourceFiles/tests/test_look_linux.py b/sourceFiles/tests/test_look_linux.py
new file mode 100644
index 0000000..a656e0c
--- /dev/null
+++ b/sourceFiles/tests/test_look_linux.py
@@ -0,0 +1,71 @@
+"""
+Light and dark on Linux: the desktop is asked once.
+
+CustomTkinter's own "system" mode asks again every 30 ms, and on Linux each
+question starts a gsettings process. So this app never leaves it in that
+mode: theme.apply_appearance asks once and sets light or dark.
+"""
+import subprocess
+
+import pytest
+
+pytest.importorskip("customtkinter")
+
+import customtkinter as ctk
+from customtkinter.windows.widgets.appearance_mode import AppearanceModeTracker
+
+import theme
+
+
+@pytest.fixture(autouse=True)
+def put_back():
+    before = ctk.get_appearance_mode()
+    yield
+    ctk.set_appearance_mode(before)
+
+
+def test_importing_the_theme_does_not_leave_system_mode():
+    assert AppearanceModeTracker.appearance_mode_set_by != "system"
+
+
+@pytest.mark.parametrize("dark,shown", [(True, "Dark"), (False, "Light")])
+def test_system_is_settled_once(monkeypatch, dark, shown):
+    asked = []
+    monkeypatch.setattr(theme, "desktop_is_dark",
+                        lambda: asked.append(1) or dark)
+    theme.apply_appearance("system")
+    assert ctk.get_appearance_mode() == shown and asked == [1]
+    assert AppearanceModeTracker.appearance_mode_set_by != "system"
+
+
+@pytest.mark.parametrize("mode", ["light", "dark"])
+def test_a_chosen_mode_does_not_ask_the_desktop(monkeypatch, mode):
+    monkeypatch.setattr(theme, "desktop_is_dark",
+                        lambda: pytest.fail("asked the desktop"))
+    theme.apply_appearance(mode)
+    assert ctk.get_appearance_mode() == mode.capitalize()
+
+
+def _gsettings(answers):
+    """A stand-in for subprocess.run that answers per key."""
+    def run(command, **options):
+        assert options.get("timeout") == 2
+        reply = answers[command[-1]]
+        if isinstance(reply, Exception):
+            raise reply
+        return subprocess.CompletedProcess(command, 0, reply.encode(), b"")
+    return run
+
+
+@pytest.mark.parametrize("answers,dark", [
+    ({"color-scheme": "'prefer-dark'\n"}, True),
+    ({"color-scheme": "'default'\n"}, False),
+    ({"color-scheme": "", "gtk-theme": "'Yaru-dark'\n"}, True),      # older
+    ({"color-scheme": "", "gtk-theme": "'Yaru'\n"}, False),
+    ({"color-scheme": "", "gtk-theme": ""}, False),                  # no answer
+    ({"color-scheme": FileNotFoundError("gsettings")}, False),       # no tool
+    ({"color-scheme": subprocess.TimeoutExpired("gsettings", 2)}, False),
+])
+def test_what_the_desktop_says(monkeypatch, answers, dark):
+    monkeypatch.setattr(subprocess, "run", _gsettings(answers))
+    assert theme.desktop_is_dark() is dark
diff --git a/sourceFiles/theme.py b/sourceFiles/theme.py
index 8cac636..c8605f3 100644
--- a/sourceFiles/theme.py
+++ b/sourceFiles/theme.py
@@ -17,7 +17,10 @@
 #: What Settings offers. "system" follows the desktop.
 APPEARANCES = ("system", "light", "dark")
 
-ctk.set_appearance_mode("system")
+# Not "system" here: on Linux CustomTkinter then asks the desktop again
+# every 30 ms, by starting a gsettings process each time. apply_appearance
+# asks once instead; the app calls it at start.
+ctk.set_appearance_mode("light")
 ctk.set_default_color_theme("green")
 
 # Rounded corners are drawn the way CustomTkinter prefers here: out of
@@ -124,9 +127,36 @@ def pick(color):
     return color
 
 
+def desktop_is_dark():
+    """
+    Whether the desktop asks for dark, from gsettings: the colour scheme,
+    and the theme's name on older desktops. False when it cannot say, and
+    it gets two seconds to answer.
+    """
+    import subprocess
+    for key in ("color-scheme", "gtk-theme"):
+        try:
+            answer = subprocess.run(
+                ["gsettings", "get", "org.gnome.desktop.interface", key],
+                capture_output=True, timeout=2).stdout.decode()
+        except Exception:
+            return False
+        if answer.strip():
+            return "-dark" in answer.lower()
+    return False
+
+
 def apply_appearance(mode):
-    """Switch to "system", "light" or "dark"; anything else means system."""
-    ctk.set_appearance_mode(mode if mode in APPEARANCES else "system")
+    """
+    Switch to "system", "light" or "dark"; anything else means system.
+
+    "system" is settled here, once: the desktop is asked and the answer is
+    set as light or dark. So a desktop that changes while the app runs is
+    followed at the next start (or by choosing in Settings).
+    """
+    if mode not in ("light", "dark"):
+        mode = "dark" if desktop_is_dark() else "light"
+    ctk.set_appearance_mode(mode)
 
 
 def strength_color(name):
diff --git a/sourceFiles/version.py b/sourceFiles/version.py
index b422354..49285ba 100644
--- a/sourceFiles/version.py
+++ b/sourceFiles/version.py
@@ -12,7 +12,7 @@
 
 import re
 
-__version__ = "1.1.0-alpha.2"
+__version__ = "1.1.0-alpha.3"
 
 #: The container a 3.0 account's vaults are written in (account_crypto).
 VAULT_FORMAT = "PMV3"