Add a secondary brand colour for clubs

Mirrors primary_color: a club-picked hex highlight used for accents like
the avatar-initials badge, with a computed readable text colour so a
pale pick doesn't produce white-on-yellow text. The shared contrast math
moves into _content_color_for so both colours use the same rule.

club/migrations/0014_club_secondary_color.py

@@ -0,0 +1,19 @@
+# Generated by Django 6.0.6 on 2026-07-24 16:30
+
+import django.core.validators
+from django.db import migrations, models
+
+
+class Migration(migrations.Migration):
+
+    dependencies = [
+        ('club', '0013_club_created_club_modified_clubmembership_created_and_more'),
+    ]
+
+    operations = [
+        migrations.AddField(
+            model_name='club',
+            name='secondary_color',
+            field=models.CharField(blank=True, help_text="Hex colour for highlights on the club's pages, e.g. avatar initials. Defaults to the theme's secondary colour.", max_length=7, validators=[django.core.validators.RegexValidator('^#[0-9a-fA-F]{6}$', 'Enter a colour as a hex value, e.g. #be185d.')], verbose_name='secondary colour'),
+        ),
+    ]

club/models.py

@@ -40,6 +40,14 @@ class Club(UUIDModel):
         help_text=_("Hex colour for buttons and links on the club's pages, e.g. #1e40af."),
     )
 
+    secondary_color = models.CharField(
+        _("secondary colour"),
+        max_length=7,
+        blank=True,
+        validators=[RegexValidator(r"^#[0-9a-fA-F]{6}$", _("Enter a colour as a hex value, e.g. #be185d."))],
+        help_text=_("Hex colour for highlights on the club's pages, e.g. avatar initials. Defaults to the theme's secondary colour."),
+    )
+
     archived_at = models.DateTimeField(_("archived at"), null=True, blank=True, help_text=_("Archived clubs stop resolving on their subdomain, but their data is retained."))
 
     objects = ClubManager()
@@ -69,19 +77,29 @@ class Club(UUIDModel):
 
     @property
     def primary_content_color(self) -> str:
-        """Readable text colour to sit *on* ``primary_color``.
+        """Readable text colour to sit *on* ``primary_color``. See ``_content_color_for``."""
+        return self._content_color_for(self.primary_color)
+
+    @property
+    def secondary_content_color(self) -> str:
+        """Readable text colour to sit *on* ``secondary_color``. See ``_content_color_for``."""
+        return self._content_color_for(self.secondary_color)
+
+    @staticmethod
+    def _content_color_for(hex_color: str) -> str:
+        """Black or white, whichever reads on ``hex_color``.
 
         A club picking a pale yellow would otherwise get white-on-yellow buttons.
         Relative luminance per WCAG, with its 0.179 threshold for black vs white.
         """
-        if not self.primary_color:
+        if not hex_color:
             return ""
 
         def channel(value: int) -> float:
             fraction = value / 255
             return fraction / 12.92 if fraction <= 0.04045 else ((fraction + 0.055) / 1.055) ** 2.4
 
-        red, green, blue = (channel(int(self.primary_color[index : index + 2], 16)) for index in (1, 3, 5))
+        red, green, blue = (channel(int(hex_color[index : index + 2], 16)) for index in (1, 3, 5))
         luminance = 0.2126 * red + 0.7152 * green + 0.0722 * blue
 
         return "#000000" if luminance > 0.179 else "#ffffff"

club/tests.py

@@ -1018,6 +1018,15 @@ class BrandingTests(TestCase):
     def test_no_colour_means_no_override(self):
         self.assertNotContains(self.login_page("ajax-united.rosterchief.app"), "--color-primary")
 
+    def test_a_club_secondary_colour_overrides_the_theme(self):
+        self.club.secondary_color = "#be185d"
+        self.club.save()
+
+        self.assertContains(self.login_page("ajax-united.rosterchief.app"), "--color-secondary: #be185d")
+
+    def test_no_secondary_colour_means_no_override(self):
+        self.assertNotContains(self.login_page("ajax-united.rosterchief.app"), "--color-secondary")
+
 
 class ClubBrandingModelTests(TestCase):
     def test_initials_use_the_first_two_words(self):