@@ -105,9 +105,13 @@ def _is_color_like(color: Any) -> bool:
 
 
 def _make_continuous_mappable(vmin: float, vmax: float, cmap: Any) -> ScalarMappable:
-    """Build a ``ScalarMappable`` for a continuous colorbar, with a ±0.5 fallback when ``vmin == vmax``."""
+    """Build a ``ScalarMappable`` for a continuous colorbar.
+
+    A degenerate ``vmin == vmax`` falls back to ``[0, 1]`` — the same rule as
+    :func:`_resolve_continuous_norm`, so the colorbar agrees with the pixel mapping.
+    """
     if vmin == vmax:
-        vmin, vmax = vmin - 0.5, vmax + 0.5
+        vmin, vmax = 0.0, 1.0
     return ScalarMappable(norm=Normalize(vmin=vmin, vmax=vmax), cmap=cmap)
 
 
 
@@ -888,6 +888,14 @@ def test_degenerate_range_resets_to_unit_interval(self):
         norm = _resolve_continuous_norm(np.array([5.0, 5.0, 5.0]), self._params())
         assert (norm.vmin, norm.vmax) == (0.0, 1.0)
 
+    def test_degenerate_clim_matches_colorbar_mappable(self):
+        # pixel norm and the (datashader) colorbar mappable must agree on a constant column
+        from spatialdata_plot.pl._color import _make_continuous_mappable, _resolve_continuous_norm
+
+        norm = _resolve_continuous_norm(np.array([5.0, 5.0]), self._params())
+        mappable = _make_continuous_mappable(5.0, 5.0, self._params().cmap)
+        assert (norm.vmin, norm.vmax) == (mappable.norm.vmin, mappable.norm.vmax) == (0.0, 1.0)
+
     def test_degenerate_lognorm_is_left_untouched(self):
         # LogNorm domain excludes 0, so the degenerate reset must not fire for it
         from matplotlib.colors import LogNorm