diff --git a/src/napari_spatialdata/_widgets.py b/src/napari_spatialdata/_widgets.py
index 5431036f..7cab1d64 100644
--- a/src/napari_spatialdata/_widgets.py
+++ b/src/napari_spatialdata/_widgets.py
@@ -18,7 +18,6 @@
 from napari.viewer import Viewer
 from qtpy import QtCore, QtWidgets
 from qtpy.QtCore import Qt, Signal
-from scanpy.plotting._utils import _set_colors_for_categorical_obs
 from sklearn.preprocessing import MinMaxScaler
 from spatialdata._types import ArrayLike
 from superqt import QRangeSlider
@@ -26,6 +25,14 @@
 from vispy.color.colormap import Colormap, MatplotlibColormap
 from vispy.scene.widgets import ColorBarWidget
 
+# See https://github.com/scverse/squidpy/issues/1061 for more details.
+# Scanpy 0.11.x-0.12.x renamed set_default_colors_for_categorical_obs to _set_default_colors_for_categorical_obs
+# and then changed it back. Try underscore version first, fall back to non-underscore.
+try:
+    from scanpy.plotting._utils import _set_colors_for_categorical_obs as set_colors_for_categorical_obs
+except ImportError:
+    from scanpy.plotting._utils import set_colors_for_categorical_obs
+
 from napari_spatialdata._model import DataModel
 from napari_spatialdata.utils._utils import _min_max_norm, get_napari_version
 
@@ -213,7 +220,7 @@ def _(self, vec: pd.Series, **kwargs: Any) -> dict[str, Any]:
         if self._attr != "columns_df":
             if vec_color_name not in self.model.adata.uns:
                 colorer = AnnData(shape=(len(vec), 0), obs=pd.DataFrame(index=vec.index, data={"vec": vec}))
-                _set_colors_for_categorical_obs(colorer, "vec", palette="tab20")
+                set_colors_for_categorical_obs(colorer, "vec", palette="tab20")
                 colors = colorer.uns["vec_colors"]
                 color_dict = dict(zip(vec.cat.categories, colors, strict=False))
                 color_dict.update({np.nan: "#808080ff"})
@@ -224,7 +231,7 @@ def _(self, vec: pd.Series, **kwargs: Any) -> dict[str, Any]:
             df = layer.metadata["_columns_df"]
             if vec_color_name not in df.columns:
                 colorer = AnnData(shape=(len(vec), 0), obs=pd.DataFrame(index=vec.index, data={"vec": vec}))
-                _set_colors_for_categorical_obs(colorer, "vec", palette="tab20")
+                set_colors_for_categorical_obs(colorer, "vec", palette="tab20")
                 colors = colorer.uns["vec_colors"]
                 color_dict = dict(zip(vec.cat.categories, colors, strict=False))
                 color_dict.update({np.nan: "#808080ff"})
diff --git a/tests/conftest.py b/tests/conftest.py
index e4f46808..9329ad51 100644
--- a/tests/conftest.py
+++ b/tests/conftest.py
@@ -1,6 +1,15 @@
 from __future__ import annotations
 
+# MUST set environment variables BEFORE any Qt/napari/vispy imports
+# to enable headless mode in CI environments (Ubuntu/Linux without display)
 import os
+import sys
+
+# Only use offscreen on Linux - macOS doesn't support the offscreen Qt platform plugin
+if sys.platform == "linux":
+    os.environ.setdefault("QT_QPA_PLATFORM", "offscreen")
+
+os.environ.setdefault("NAPARI_HEADLESS", "1")
 import random
 import string
 from abc import ABC, ABCMeta