From 6440153c744a796e4bbd2140cda9e86b1e4432ef Mon Sep 17 00:00:00 2001
From: Gavin Ridley <gavin.keith.ridley@gmail.com>
Date: Fri, 21 Apr 2023 16:37:48 -0400
Subject: [PATCH 1/2] pass 0-1 RGB value to matplotlib in universe plot legend

---
 openmc/universe.py | 17 +++++++++++++++--
 1 file changed, 15 insertions(+), 2 deletions(-)

diff --git a/openmc/universe.py b/openmc/universe.py
index 67296dda8c..02ce1609c3 100644
--- a/openmc/universe.py
+++ b/openmc/universe.py
@@ -426,7 +426,8 @@ class Universe(UniverseBase):
             if outline:
                 # Combine R, G, B values into a single int
                 rgb = (img * 256).astype(int)
-                image_value = (rgb[..., 0] << 16) + (rgb[..., 1] << 8) + (rgb[..., 2])
+                image_value = (rgb[..., 0] << 16) + \
+                    (rgb[..., 1] << 8) + (rgb[..., 2])
 
                 axes.contour(
                     image_value,
@@ -462,7 +463,19 @@ class Universe(UniverseBase):
 
                     # this works whether we're doing cells or materials
                     label = key.name if key.name != '' else key.id
-                    key_patch = mpatches.Patch(color=color, label=label)
+
+                    # matplotlib takes RGB on 0-1 scale rather than 0-255. at
+                    # this point PlotBase has already checked that 3-tuple
+                    # based colors are already valid, so if the length is three
+                    # then we know it just needs to be converted to the 0-1
+                    # format.
+                    if len(color) == 3 and not isinstance(color, str):
+                        scaled_color = (
+                            color[0]/255, color[1]/255, color[2]/255)
+                    else:
+                        scaled_color = color
+
+                    key_patch = mpatches.Patch(color=scaled_color, label=label)
                     patches.append(key_patch)
 
                 axes.legend(handles=patches, **legend_kwargs)

From af5596b6cf519e2c0377c8b41010a9518387f69a Mon Sep 17 00:00:00 2001
From: Jonathan Shimwell <mail@jshimwell.com>
Date: Wed, 26 Apr 2023 16:14:14 +0100
Subject: [PATCH 2/2] plt test includes legend with rgb color

---
 tests/unit_tests/test_universe.py | 25 ++++++++++++++++---------
 1 file changed, 16 insertions(+), 9 deletions(-)

diff --git a/tests/unit_tests/test_universe.py b/tests/unit_tests/test_universe.py
index 1bfbbf7ff8..cb4f2b7030 100644
--- a/tests/unit_tests/test_universe.py
+++ b/tests/unit_tests/test_universe.py
@@ -48,18 +48,25 @@ def test_bounding_box():
     assert_unbounded(u)
 
 
-def test_plot(run_in_tmpdir, sphere_model):
-    m = sphere_model.materials[0]
-    univ = sphere_model.geometry.root_universe
+def test_plot(run_in_tmpdir):
+
+    pincell = openmc.examples.pwr_pin_cell()
+    materials = pincell.materials
+
+    mat_colors = {
+        materials[0]: (200, 1, 1),
+        materials[1]: "gray",
+        materials[2]: "limegreen"
+    }
 
-    colors = {m: 'limegreen'}
     for basis in ('xy', 'yz', 'xz'):
-        univ.plot(
-            basis=basis,
+        pincell.geometry.root_universe.plot(
+            colors=mat_colors,
+            color_by="material",
+            legend=True,
             pixels=(10, 10),
-            color_by='material',
-            colors=colors,
-            outline=True,
+            basis=basis,
+            outline=True
         )