fix: handle 3-digit shorthand hex in hex_to_rgb

Expand 3-char hex codes (e.g. #FFF) to 6-char before parsing.
Fixes both _plotly_utils and matplotlylib copies.

Closes #5661

Author: genrichez

_plotly_utils/colors/__init__.py

@@ -757,6 +757,8 @@ def hex_to_rgb(value):
     :rtype (tuple) (r_value, g_value, b_value): tuple of rgb values
     """
     value = value.lstrip("#")
+    if len(value) == 3:
+        value = "".join(c * 2 for c in value)
     hex_total_length = len(value)
     rgb_section_length = hex_total_length // 3
     return tuple(

plotly/matplotlylib/mpltools.py

@@ -117,6 +117,8 @@ def hex_to_rgb(value):
 
     """
     value = value.lstrip("#")
+    if len(value) == 3:
+        value = "".join(c * 2 for c in value)
     lv = len(value)
     return tuple(int(value[i : i + lv // 3], 16) for i in range(0, lv, lv // 3))
 

tests/test_plotly_utils/colors/test_color_conversions.py

@@ -12,6 +12,15 @@ def test_hex_to_rgb_basic_values():
     assert hex_to_rgb("#aabbcc") == (170, 187, 204)
 
 
+def test_hex_to_rgb_shorthand_3_digit():
+    assert hex_to_rgb("#fff") == (255, 255, 255)
+    assert hex_to_rgb("#000") == (0, 0, 0)
+    assert hex_to_rgb("#abc") == (170, 187, 204)
+    assert hex_to_rgb("#f00") == (255, 0, 0)
+    assert hex_to_rgb("#0f0") == (0, 255, 0)
+    assert hex_to_rgb("#00f") == (0, 0, 255)
+
+
 def test_label_rgb_formats_tuple():
     assert label_rgb((255, 0, 0)) == "rgb(255, 0, 0)"
     assert label_rgb((1, 2, 3)) == "rgb(1, 2, 3)"