matplotlib · NelleV · Aug 31, 2019 · Aug 28, 2019 · Aug 30, 2019
diff --git a/doc/users/next_whats_new/shorthand_hex_colors.rst b/doc/users/next_whats_new/shorthand_hex_colors.rst
@@ -0,0 +1,6 @@
+3-digit and 4-digit hex colors
+------------------------------
+
+Colors can now be specified using 3-digit or 4-digit hex colors, shorthand for
+the colors obtained by duplicating each character, e.g. ``#123`` is equivalent to
+``#112233`` and  ``#123a`` is equivalent to ``#112233aa``.
diff --git a/lib/matplotlib/colors.py b/lib/matplotlib/colors.py
@@ -40,6 +40,10 @@
   interval ``[0, 1]`` (e.g., ``(0.1, 0.2, 0.5)`` or ``(0.1, 0.2, 0.5, 0.3)``);
 * a hex RGB or RGBA string (e.g., ``'#0f0f0f'`` or ``'#0f0f0f80'``;
   case-insensitive);
+* a shorthand hex RGB or RGBA string, equivalent to the hex RGB or RGBA
+  string obtained by duplicating each character, (e.g., ``'#abc'``, equivalent
+  to ``'#aabbcc'``, or ``'#abcd'``, equivalent to ``'#aabbccdd'``;
+  case-insensitive);
 * a string representation of a float value in ``[0, 1]`` inclusive for gray
   level (e.g., ``'0.5'``);
 * one of ``{'b', 'g', 'r', 'c', 'm', 'y', 'k', 'w'}``, they are the single
@@ -215,20 +219,34 @@ def _to_rgba_no_colorcycle(c, alpha=None):
                         "%(since)s and will be removed %(removal)s; please "
                         "use lowercase instead.")
     if isinstance(c, str):
-        # hex color with no alpha.
+        # hex color in #rrggbb format.
         match = re.match(r"\A#[a-fA-F0-9]{6}\Z", c)
         if match:
             return (tuple(int(n, 16) / 255
                           for n in [c[1:3], c[3:5], c[5:7]])
                     + (alpha if alpha is not None else 1.,))
-        # hex color with alpha.
+        # hex color in #rgb format, shorthand for #rrggbb.
+        match = re.match(r"\A#[a-fA-F0-9]{3}\Z", c)
+        if match:
+            return (tuple(int(n, 16) / 255
+                          for n in [c[1]*2, c[2]*2, c[3]*2])
+                    + (alpha if alpha is not None else 1.,))
+        # hex color with alpha in #rrggbbaa format.
         match = re.match(r"\A#[a-fA-F0-9]{8}\Z", c)
         if match:
             color = [int(n, 16) / 255
                      for n in [c[1:3], c[3:5], c[5:7], c[7:9]]]
             if alpha is not None:
                 color[-1] = alpha
             return tuple(color)
+        # hex color with alpha in #rgba format, shorthand for #rrggbbaa.
+        match = re.match(r"\A#[a-fA-F0-9]{4}\Z", c)
+        if match:
+            color = [int(n, 16) / 255
+                     for n in [c[1]*2, c[2]*2, c[3]*2, c[4]*2]]
+            if alpha is not None:
+                color[-1] = alpha
+            return tuple(color)
         # string gray.
         try:
             c = float(c)

diff --git a/lib/matplotlib/tests/test_colors.py b/lib/matplotlib/tests/test_colors.py
@@ -910,3 +910,8 @@ def __add__(self, other):
 def test_same_color():
     assert mcolors.same_color('k', (0, 0, 0))
     assert not mcolors.same_color('w', (1, 1, 0))
+
+
+def test_hex_shorthand_notation():
+    assert mcolors.same_color("#123", "#112233")
+    assert mcolors.same_color("#123a", "#112233aa")
diff --git a/tutorials/colors/colors.py b/tutorials/colors/colors.py
@@ -9,6 +9,10 @@
   interval ``[0, 1]`` (e.g., ``(0.1, 0.2, 0.5)`` or ``(0.1, 0.2, 0.5, 0.3)``);
 * a hex RGB or RGBA string (e.g., ``'#0f0f0f'`` or ``'#0f0f0f80'``;
   case-insensitive);
+* a shorthand hex RGB or RGBA string, equivalent to the hex RGB or RGBA
+  string obtained by duplicating each character, (e.g., ``'#abc'``, equivalent
+  to ``'#aabbcc'``, or ``'#abcd'``, equivalent to ``'#aabbccdd'``;
+  case-insensitive);
 * a string representation of a float value in ``[0, 1]`` inclusive for gray
   level (e.g., ``'0.5'``);
 * one of ``{'b', 'g', 'r', 'c', 'm', 'y', 'k', 'w'}``, they are the single