ENH: Add Petroff 6 and 8 color cycle style sheets

* Add the 6 color and the 8 color Petroff color cycles from
  Matthew A. Petroff, Accessible Color Sequences for Data Visualization
  https://arxiv.org/abs/2107.02270.
  The 10 color cycle was added in PR 27851 which landed in Matplotlib v3.10.0.

Author: matthewfeickert

lib/matplotlib/_cm.py

@@ -1365,6 +1365,29 @@ def _gist_yarg(x): return 1 - x
     (0.8509803921568627,  0.8509803921568627,  0.8509803921568627  ),  # d9d9d9
 )
 
+# Colorblind accessible palettes from
+# Matthew A. Petroff, Accessible Color Sequences for Data Visualization
+# https://arxiv.org/abs/2107.02270
+
+_petroff6_data = (
+    (0.3411764705882353,  0.5647058823529412,  0.9882352941176471),    # 5790fc
+    (0.9725490196078431,  0.611764705882353,   0.12549019607843137),   # f89c20
+    (0.8941176470588236,  0.1450980392156863,  0.21176470588235294),   # e42536
+    (0.5882352941176471,  0.2901960784313726,  0.5450980392156862),    # 964a8b
+    (0.611764705882353,   0.611764705882353,   0.6313725490196078),    # 9c9ca1
+    (0.47843137254901963, 0.12941176470588237, 0.8666666666666667),    # 7a21dd
+)
+
+_petroff8_data = (
+    (0.09411764705882353, 0.27058823529411763, 0.984313725490196),     # 1845fb
+    (1.0,                 0.3686274509803922,  0.00784313725490196),   # ff5e02
+    (0.788235294117647,   0.12156862745098039, 0.08627450980392157),   # c91f16
+    (0.7843137254901961,  0.28627450980392155, 0.6627450980392157),    # c849a9
+    (0.6784313725490196,  0.6784313725490196,  0.49019607843137253),   # adad7d
+    (0.5254901960784314,  0.7843137254901961,  0.8666666666666667),    # 86c8dd
+    (0.3411764705882353,  0.5529411764705883,  1.0),                   # 578dff
+    (0.396078431372549,   0.38823529411764707, 0.39215686274509803),   # 656364
+)
 
 _petroff10_data = (
     (0.24705882352941178, 0.5647058823529412,  0.8549019607843137),    # 3f90da

lib/matplotlib/colors.py

@@ -131,6 +131,8 @@ class ColorSequenceRegistry(Mapping):
         'Set1': _cm._Set1_data,
         'Set2': _cm._Set2_data,
         'Set3': _cm._Set3_data,
+        'petroff6': _cm._petroff6_data,
+        'petroff8': _cm._petroff8_data,
         'petroff10': _cm._petroff10_data,
     }
 

lib/matplotlib/mpl-data/stylelib/petroff6.mplstyle

@@ -0,0 +1,5 @@
+# Color cycle survey palette from Petroff (2021):
+# https://arxiv.org/abs/2107.02270
+# https://github.com/mpetroff/accessible-color-cycles
+axes.prop_cycle: cycler('color', ['5790fc', 'f89c20', 'e42536', '964a8b', '9c9ca1', '7a21dd'])
+patch.facecolor: 5790fc

lib/matplotlib/mpl-data/stylelib/petroff8.mplstyle

@@ -0,0 +1,5 @@
+# Color cycle survey palette from Petroff (2021):
+# https://arxiv.org/abs/2107.02270
+# https://github.com/mpetroff/accessible-color-cycles
+axes.prop_cycle: cycler('color', ['1845fb', 'ff5e02', 'c91f16', 'c849a9', 'adad7d', '86c8dd', '578dff', '656364'])
+patch.facecolor: 1845fb