From 34488dd6ba07c4741a9262dece3de388de654148 Mon Sep 17 00:00:00 2001
From: Roberto Moura <roberto@ffmoura.com>
Date: Tue, 11 Aug 2026 10:07:30 +0000
Subject: [PATCH] Fix boxplot conversion by mapping 'none' colors to
 transparent rgba

---
 plotly/matplotlylib/renderer.py            | 38 +++++++++++++++++-----
 plotly/matplotlylib/tests/test_renderer.py |  9 +++++
 2 files changed, 39 insertions(+), 8 deletions(-)

diff --git a/plotly/matplotlylib/renderer.py b/plotly/matplotlylib/renderer.py
index 7c2340180cc..c14a8e78d0f 100644
--- a/plotly/matplotlylib/renderer.py
+++ b/plotly/matplotlylib/renderer.py
@@ -14,6 +14,24 @@
 from plotly.matplotlylib import mpltools
 
 
+def _export_color(color):
+    """Export a matplotlib color for use as a plotly color.
+
+    matplotlib uses "none" for fully transparent colors, which plotly does not
+    accept, so transparent colors are exported as transparent black.
+    Colors already exported by the mplexporter (hex or rgba strings) are
+    passed through unchanged.
+    """
+    if isinstance(color, str):
+        return "rgba(0,0,0,0)" if color == "none" else color
+    if isinstance(color, (list, tuple)) and all(
+        isinstance(c, str) for c in color
+    ):
+        return [_export_color(c) for c in color]
+    bgcolor = export_color(color)
+    return "rgba(0,0,0,0)" if bgcolor == "none" else bgcolor
+
+
 class PlotlyRenderer(Renderer):
     """A renderer class inheriting from base for rendering mpl plots in plotly.
 
@@ -317,7 +335,7 @@ def draw_bar(self, coll):
             yaxis="y{0}".format(self.axis_ct),
             opacity=trace[0]["alpha"],  # TODO: get all alphas if array?
             marker=go.bar.Marker(
-                color=trace[0]["facecolor"],  # TODO: get all
+                color=_export_color(trace[0]["facecolor"]),  # TODO: get all
                 line=dict(width=trace[0]["edgewidth"]),
             ),
         )  # TODO ditto
@@ -379,9 +397,13 @@ def draw_marked_line(self, **props):
             self.msg += "... with just markers\n"
             mode = "markers"
         if props["linestyle"]:
-            color = mpltools.merge_color_and_opacity(
-                props["linestyle"]["color"], props["linestyle"]["alpha"]
-            )
+            if props["linestyle"]["color"] == "none":
+                # a fully transparent line; plotly rejects "none" as a color
+                color = "rgba(0,0,0,0)"
+            else:
+                color = mpltools.merge_color_and_opacity(
+                    props["linestyle"]["color"], props["linestyle"]["alpha"]
+                )
 
             if props["coordinates"] == "data":
                 line = go.scatter.Line(
@@ -401,22 +423,22 @@ def draw_marked_line(self, **props):
             if props["coordinates"] == "data":
                 marker = go.scatter.Marker(
                     opacity=props["markerstyle"]["alpha"],
-                    color=props["markerstyle"]["facecolor"],
+                    color=_export_color(props["markerstyle"]["facecolor"]),
                     symbol=mpltools.convert_symbol(props["markerstyle"]["marker"]),
                     size=props["markerstyle"]["markersize"],
                     line=dict(
-                        color=props["markerstyle"]["edgecolor"],
+                        color=_export_color(props["markerstyle"]["edgecolor"]),
                         width=props["markerstyle"]["edgewidth"],
                     ),
                 )
             else:
                 shape = dict(
                     opacity=props["markerstyle"]["alpha"],
-                    fillcolor=props["markerstyle"]["facecolor"],
+                    fillcolor=_export_color(props["markerstyle"]["facecolor"]),
                     symbol=mpltools.convert_symbol(props["markerstyle"]["marker"]),
                     size=props["markerstyle"]["markersize"],
                     line=dict(
-                        color=props["markerstyle"]["edgecolor"],
+                        color=_export_color(props["markerstyle"]["edgecolor"]),
                         width=props["markerstyle"]["edgewidth"],
                     ),
                 )
diff --git a/plotly/matplotlylib/tests/test_renderer.py b/plotly/matplotlylib/tests/test_renderer.py
index 0d63e4815b9..18d9a8f627d 100644
--- a/plotly/matplotlylib/tests/test_renderer.py
+++ b/plotly/matplotlylib/tests/test_renderer.py
@@ -1,3 +1,4 @@
+import numpy as np
 import matplotlib.pyplot as plt
 import plotly.tools as tls
 
@@ -84,3 +85,11 @@ def test_multiple_traces_native_legend():
     assert plotly_fig.data[0].mode == "lines"
     assert plotly_fig.data[1].mode == "markers"
     assert plotly_fig.data[2].mode == "lines+markers"
+
+
+def test_boxplot_converts_with_none_marker_facecolor():
+    """Boxplot outlier markers use facecolor 'none', which plotly rejects."""
+    fig, ax = plt.subplots()
+    ax.boxplot(np.random.randn(100, 4))
+    plotly_fig = tls.mpl_to_plotly(fig)  # used to raise ValueError
+    assert len(plotly_fig.data) > 0