fix(welcome): follow color mode changes in subdued texts

datalab/gui/main.py

@@ -91,6 +91,7 @@
 from datalab.webapi.actions import WebApiActions
 from datalab.widgets import instconfviewer
 from datalab.widgets import status as dl_status
+from datalab.widgets.expandabletext import refresh_subdued_colors
 
 if TYPE_CHECKING:
     from typing import Literal
@@ -2390,9 +2391,10 @@ def _about(self) -> None:  # pragma: no cover
         )
 
     def _update_extra_color_mode(self) -> None:
-        """Update the macro panel color mode"""
+        """Update the macro panel color mode and the subdued text colors"""
         if self.macropanel is not None:
             self.macropanel.update_color_mode()
+        refresh_subdued_colors()
 
     # Settings changes are intentionally dispatched in one place because each
     # option may trigger a specific live UI update or panel refresh.

datalab/tests/features/common/welcome_unit_test.py

@@ -9,6 +9,8 @@
 from types import SimpleNamespace
 
 import numpy as np
+from guidata import qthelpers as guidata_qth
+from plotpy import config as plotpy_config
 from qtpy import QtCore as QC
 from qtpy import QtGui as QG
 from qtpy import QtWidgets as QW
@@ -120,6 +122,38 @@ def create_gaussian(menu: QW.QMenu, *_args) -> None:
             Conf.welcome_on_startup.set(initial)
 
 
+def test_welcome_page_follows_color_mode(monkeypatch) -> None:
+    """Subdued texts remain legible when the color mode is switched at runtime"""
+    # Switching the color mode changes these globals: restore them at teardown
+    monkeypatch.setenv(guidata_qth.ENV_COLOR_MODE, guidata_qth.get_color_mode())
+    monkeypatch.setattr(guidata_qth, "CURRENT_THEME", guidata_qth.CURRENT_THEME)
+    initial_mode = Conf.color_mode.get()
+    description = _("Generate a 1D signal or 2D image from a template.")
+    with datalab_test_app_context(console=False) as win:
+        page = win.welcomepanel
+        labels = [page.start_title] + [
+            label
+            for label in page.entries["create"].findChildren(QW.QLabel)
+            if label.text() == description
+        ]
+        assert len(labels) == 2
+        try:
+            # Light to dark, then dark to light
+            for mode in ("light", "dark", "light"):
+                Conf.color_mode.set(mode)
+                win._update_color_mode()  # pylint: disable=protected-access
+                palette = QW.QApplication.instance().palette()
+                window = palette.color(QG.QPalette.Window).lightness()
+                for label in labels:
+                    text = label.palette().color(QG.QPalette.WindowText)
+                    alpha = text.alphaF()
+                    lightness = alpha * text.lightness() + (1 - alpha) * window
+                    assert abs(lightness - window) > 64, (mode, label.text())
+        finally:
+            Conf.color_mode.set(initial_mode)
+            plotpy_config.set_plotpy_color_mode(guidata_qth.LIGHT)
+
+
 def _application_plugin(
     plugin_id: str,
     tiles: tuple[WelcomeTile, ...] | Exception,

datalab/widgets/expandabletext.py

@@ -33,6 +33,9 @@
 #: Default left indent in pixels
 DEFAULT_INDENT: int = 20
 
+#: Dynamic property marking the widgets with a subdued text color
+SUBDUED_PROPERTY: str = "datalab_subdued"
+
 
 # --- Palette helpers (public — reused by other modules) --------------------------
 
@@ -52,18 +55,33 @@ def apply_palette_color(widget: QW.QWidget, color: QG.QColor) -> None:
 def apply_subdued_color(widget: QW.QWidget) -> None:
     """Apply a subdued/secondary text color on *widget*.
 
-    Uses the ``QPalette.PlaceholderText`` role (Qt 5.12+) which provides a
-    theme-native "dimmed" color.  Sets both ``WindowText`` (for ``QLabel``)
-    and ``Text`` (for ``QTextBrowser`` / ``QTextEdit``) roles.
+    The application ``WindowText`` (for ``QLabel``) and ``Text`` (for
+    ``QTextBrowser`` / ``QTextEdit``) colors are dimmed to half opacity, like Qt
+    placeholder texts. The widget is marked so that :func:`refresh_subdued_colors`
+    can follow color mode changes.
 
     Args:
         widget: Target widget
     """
-    subdued = QW.QApplication.instance().palette().color(QG.QPalette.PlaceholderText)
+    app_palette = QW.QApplication.instance().palette()
     palette = widget.palette()
-    palette.setColor(QG.QPalette.WindowText, subdued)
-    palette.setColor(QG.QPalette.Text, subdued)
+    for role in (QG.QPalette.WindowText, QG.QPalette.Text):
+        color = QG.QColor(app_palette.color(role))
+        color.setAlpha(128)
+        palette.setColor(role, color)
     widget.setPalette(palette)
+    widget.setProperty(SUBDUED_PROPERTY, True)
+
+
+def refresh_subdued_colors() -> None:
+    """Update the subdued text colors after an application palette change.
+
+    Subdued colors are set explicitly on widgets, so they do not follow the
+    application palette by themselves.
+    """
+    for widget in QW.QApplication.allWidgets():
+        if widget.property(SUBDUED_PROPERTY):
+            apply_subdued_color(widget)
 
 
 # --- Internal helpers ------------------------------------------------------------