diff --git a/lib/matplotlib/axes/_axes.py b/lib/matplotlib/axes/_axes.py
index 876496ef81f0..9ed0254b81ff 100644
--- a/lib/matplotlib/axes/_axes.py
+++ b/lib/matplotlib/axes/_axes.py
@@ -4394,7 +4394,7 @@ def invalid_shape_exception(csize, xsize):
                     c_is_mapped = True
                 else:  # Wrong size; it must not be intended for mapping.
                     if c.shape in ((3,), (4,)):
-                        _log.warning(
+                        _api.warn_external(
                             "*c* argument looks like a single numeric RGB or "
                             "RGBA sequence, which should be avoided as value-"
                             "mapping will have precedence in case its length "
diff --git a/lib/matplotlib/tests/test_axes.py b/lib/matplotlib/tests/test_axes.py
index 1221eb219ab4..8ed4066efdf7 100644
--- a/lib/matplotlib/tests/test_axes.py
+++ b/lib/matplotlib/tests/test_axes.py
@@ -1,3 +1,4 @@
+import contextlib
 from collections import namedtuple
 import datetime
 from decimal import Decimal
@@ -2638,15 +2639,17 @@ def get_next_color():
             "conversion": "^'c' argument must be a color",  # bad vals
             }
 
-        if re_key is None:
+        assert_context = (
+            pytest.raises(ValueError, match=REGEXP[re_key])
+            if re_key is not None
+            else pytest.warns(match="argument looks like a single numeric RGB")
+            if isinstance(c_case, list) and len(c_case) == 3
+            else contextlib.nullcontext()
+        )
+        with assert_context:
             mpl.axes.Axes._parse_scatter_color_args(
                 c=c_case, edgecolors="black", kwargs={}, xsize=xsize,
                 get_next_color_func=get_next_color)
-        else:
-            with pytest.raises(ValueError, match=REGEXP[re_key]):
-                mpl.axes.Axes._parse_scatter_color_args(
-                    c=c_case, edgecolors="black", kwargs={}, xsize=xsize,
-                    get_next_color_func=get_next_color)
 
     @mpl.style.context('default')
     @check_figures_equal(extensions=["png"])
@@ -6803,9 +6806,9 @@ def test_color_length_mismatch():
     fig, ax = plt.subplots()
     with pytest.raises(ValueError):
         ax.scatter(x, y, c=colors)
-    c_rgb = (0.5, 0.5, 0.5)
-    ax.scatter(x, y, c=c_rgb)
-    ax.scatter(x, y, c=[c_rgb] * N)
+    with pytest.warns(match="argument looks like a single numeric RGB"):
+        ax.scatter(x, y, c=(0.5, 0.5, 0.5))
+    ax.scatter(x, y, c=[(0.5, 0.5, 0.5)] * N)
 
 
 def test_eventplot_legend():
@@ -7688,7 +7691,8 @@ def test_2dcolor_plot(fig_test, fig_ref):
     # plot with 1D-color:
     axs = fig_test.subplots(5)
     axs[0].plot([1, 2], [1, 2], c=color.reshape(-1))
-    axs[1].scatter([1, 2], [1, 2], c=color.reshape(-1))
+    with pytest.warns(match="argument looks like a single numeric RGB"):
+        axs[1].scatter([1, 2], [1, 2], c=color.reshape(-1))
     axs[2].step([1, 2], [1, 2], c=color.reshape(-1))
     axs[3].hist(np.arange(10), color=color.reshape(-1))
     axs[4].bar(np.arange(10), np.arange(10), color=color.reshape(-1))