diff --git a/server/szurubooru/func/tag_categories.py b/server/szurubooru/func/tag_categories.py
index c5f088fe..b4da67c3 100644
--- a/server/szurubooru/func/tag_categories.py
+++ b/server/szurubooru/func/tag_categories.py
@@ -51,7 +51,7 @@ def update_category_name(category, name):
 def update_category_color(category, color):
     if not color:
         raise InvalidTagCategoryNameError('Color cannot be empty.')
-    if not re.match(r'^#?[a-z]+$', color):
+    if not re.match(r'^#?[0-9a-z]+$', color):
         raise InvalidTagCategoryNameError('Invalid color.')
     if util.value_exceeds_column_size(color, db.TagCategory.color):
         raise InvalidTagCategoryColorError('Color is too long.')