Extract warning constant and align na_color override with points

- Extract duplicated groups-ignored warning string to _GROUPS_IGNORED_WARNING
- Add col_for_color guard to na_color override, matching the points pattern

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: timtreis

src/spatialdata_plot/pl/render.py

@@ -1314,7 +1314,11 @@ def _render_labels(
 
     _, trans_data = _prepare_transformation(label, coordinate_system, ax)
 
-    na_color = render_params.color if render_params.color is not None else render_params.cmap_params.na_color
+    na_color = (
+        render_params.color
+        if col_for_color is None and render_params.color is not None
+        else render_params.cmap_params.na_color
+    )
     color_source_vector, color_vector, categorical = _set_color_source_vec(
         sdata=sdata_filt,
         element=label,

src/spatialdata_plot/pl/utils.py

@@ -94,6 +94,8 @@
 # once https://github.com/scverse/spatialdata/pull/689/ is in a release
 ColorLike = tuple[float, ...] | list[float] | str
 
+_GROUPS_IGNORED_WARNING = "Parameter 'groups' is ignored when 'color' is a literal color, not a column name."
+
 
 def _extract_scalar_value(value: Any, default: float = 0.0) -> float:
     """
@@ -2474,7 +2476,7 @@ def _validate_label_render_params(
         has_col = element_params[el]["col_for_color"] is not None
         element_params[el]["palette"] = param_dict["palette"] if has_col else None
         if not has_col and param_dict["groups"] is not None:
-            logger.warning("Parameter 'groups' is ignored when 'color' is a literal color, not a column name.")
+            logger.warning(_GROUPS_IGNORED_WARNING)
         element_params[el]["groups"] = param_dict["groups"] if has_col else None
         element_params[el]["colorbar"] = param_dict["colorbar"]
         element_params[el]["colorbar_params"] = param_dict["colorbar_params"]
@@ -2544,7 +2546,7 @@ def _validate_points_render_params(
 
         element_params[el]["palette"] = param_dict["palette"] if param_dict["col_for_color"] is not None else None
         if param_dict["col_for_color"] is None and param_dict["groups"] is not None:
-            logger.warning("Parameter 'groups' is ignored when 'color' is a literal color, not a column name.")
+            logger.warning(_GROUPS_IGNORED_WARNING)
         element_params[el]["groups"] = param_dict["groups"] if param_dict["col_for_color"] is not None else None
         element_params[el]["ds_reduction"] = param_dict["ds_reduction"]
         element_params[el]["colorbar"] = param_dict["colorbar"]
@@ -2630,7 +2632,7 @@ def _validate_shape_render_params(
 
         element_params[el]["palette"] = param_dict["palette"] if param_dict["col_for_color"] is not None else None
         if param_dict["col_for_color"] is None and param_dict["groups"] is not None:
-            logger.warning("Parameter 'groups' is ignored when 'color' is a literal color, not a column name.")
+            logger.warning(_GROUPS_IGNORED_WARNING)
         element_params[el]["groups"] = param_dict["groups"] if param_dict["col_for_color"] is not None else None
         element_params[el]["method"] = param_dict["method"]
         element_params[el]["ds_reduction"] = param_dict["ds_reduction"]