Allow to configure accent colors

src/pretix/base/settings.py

@@ -483,6 +483,14 @@ Your {event} team"""))
         'default': '#8E44B3',
         'type': str
     },
+    'theme_color_success': {
+        'default': '#50A167',
+        'type': str
+    },
+    'theme_color_danger': {
+        'default': '#D36060',
+        'type': str
+    },
     'primary_font': {
         'default': 'Open Sans',
         'type': str

src/pretix/control/forms/__init__.py

@@ -5,6 +5,7 @@ from django import forms
 from django.conf import settings
 from django.core.exceptions import ValidationError
 from django.forms.utils import from_current_timezone
+from django.utils.deconstruct import deconstructible
 from django.utils.html import conditional_escape
 from django.utils.translation import ugettext_lazy as _
 
@@ -185,3 +186,44 @@ class SplitDateTimeField(forms.SplitDateTimeField):
             result = datetime.datetime.combine(*data_list)
             return from_current_timezone(result)
         return None
+
+
+@deconstructible
+class ColorContrastValidator:
+    message = _('This color is too bright to allow for proper contrast when used for text on white ground.')
+    code = 'contrast'
+
+    def __init__(self, message=None, code=None):
+        if message is not None:
+            self.message = message
+        if code is not None:
+            self.code = code
+
+    def __call__(self, value):
+        # See https://www.w3.org/TR/2008/REC-WCAG20-20081211/#relativeluminancedef
+        fg_color = [int(str(value)[1:3], 16), int(str(value)[1:3], 16), int(str(value)[1:3], 16)]
+        bg_color = [255, 255, 255]
+        fg_lum = [
+            (float(cc) / 255) / 12.92
+            if (float(cc) / 255) < 0.03928
+            else (((float(cc) / 255) + 0.055) / 1.055) ** 2.4
+            for cc in fg_color
+        ]
+        bg_lum = [
+            (float(cc) / 255) / 12.92
+            if (float(cc) / 255) < 0.03928
+            else (((float(cc) / 255) + 0.055) / 1.055) ** 2.4
+            for cc in bg_color
+        ]
+        fg_rel_lum = 0.2126 * fg_lum[0] + 0.7152 * fg_lum[1] + 0.0722 * fg_lum[2]
+        bg_rel_lum = 0.2126 * bg_lum[0] + 0.7152 * bg_lum[1] + 0.0722 * bg_lum[2]
+        contrast_ratio = (bg_rel_lum + 0.05) / (fg_rel_lum + 0.05)
+        if contrast_ratio < 1.4:
+            raise ValidationError(self.message, code=self.code)
+
+    def __eq__(self, other):
+        return (
+            isinstance(other, ColorContrastValidator) and
+            (self.message == other.message) and
+            (self.code == other.code)
+        )

src/pretix/control/forms/event.py

@@ -22,8 +22,9 @@ from pretix.base.models.event import EventMetaValue, SubEvent
 from pretix.base.reldate import RelativeDateField, RelativeDateTimeField
 from pretix.base.settings import PERSON_NAME_SCHEMES
 from pretix.control.forms import (
-    ExtFileField, MultipleLanguagesWidget, SingleLanguageWidget, SlugWidget,
-    SplitDateTimeField, SplitDateTimePickerWidget,
+    ColorContrastValidator, ExtFileField, MultipleLanguagesWidget,
+    SingleLanguageWidget, SlugWidget, SplitDateTimeField,
+    SplitDateTimePickerWidget,
 )
 from pretix.multidomain.urlreverse import build_absolute_uri
 from pretix.plugins.banktransfer.payment import BankTransfer
@@ -935,10 +936,37 @@ class MailSettingsForm(SettingsForm):
 class DisplaySettingsForm(SettingsForm):
     primary_color = forms.CharField(
         label=_("Primary color"),
+        help_text=_("We strongly suggest to use a dark shade that has a good contrast for text on white ground."),
         required=False,
         validators=[
             RegexValidator(regex='^#[0-9a-fA-F]{6}$',
-                           message=_('Please enter the hexadecimal code of a color, e.g. #990000.'))
+                           message=_('Please enter the hexadecimal code of a color, e.g. #990000.')),
+            ColorContrastValidator()
+        ],
+        widget=forms.TextInput(attrs={'class': 'colorpickerfield'})
+    )
+    theme_color_success = forms.CharField(
+        label=_("Accent color for success"),
+        help_text=_("We strongly suggest to use a dark shade of green that has a good contrast for text on white "
+                    "ground."),
+        required=False,
+        validators=[
+            RegexValidator(regex='^#[0-9a-fA-F]{6}$',
+                           message=_('Please enter the hexadecimal code of a color, e.g. #990000.')),
+            ColorContrastValidator()
+        ],
+        widget=forms.TextInput(attrs={'class': 'colorpickerfield'})
+    )
+    theme_color_danger = forms.CharField(
+        label=_("Accent color for errors"),
+        help_text=_("We strongly suggest to use a dark shade of red that has a good contrast for text on white "
+                    "ground."),
+        required=False,
+        validators=[
+            RegexValidator(regex='^#[0-9a-fA-F]{6}$',
+                           message=_('Please enter the hexadecimal code of a color, e.g. #990000.')),
+
+            ColorContrastValidator()
         ],
         widget=forms.TextInput(attrs={'class': 'colorpickerfield'})
     )

src/pretix/control/forms/organizer.py

@@ -10,7 +10,9 @@ from pretix.api.models import WebHook
 from pretix.api.webhooks import get_all_webhook_events
 from pretix.base.forms import I18nModelForm, SettingsForm
 from pretix.base.models import Device, Organizer, Team
-from pretix.control.forms import ExtFileField, MultipleLanguagesWidget
+from pretix.control.forms import (
+    ColorContrastValidator, ExtFileField, MultipleLanguagesWidget,
+)
 from pretix.multidomain.models import KnownDomain
 from pretix.presale.style import get_fonts
 
@@ -178,7 +180,33 @@ class OrganizerDisplaySettingsForm(SettingsForm):
         required=False,
         validators=[
             RegexValidator(regex='^#[0-9a-fA-F]{6}$',
-                           message=_('Please enter the hexadecimal code of a color, e.g. #990000.'))
+                           message=_('Please enter the hexadecimal code of a color, e.g. #990000.')),
+            ColorContrastValidator()
+        ],
+        widget=forms.TextInput(attrs={'class': 'colorpickerfield'})
+    )
+    theme_color_success = forms.CharField(
+        label=_("Accent color for success"),
+        help_text=_("We strongly suggest to use a dark shade of green that has a good contrast for text on white "
+                    "ground."),
+        required=False,
+        validators=[
+            RegexValidator(regex='^#[0-9a-fA-F]{6}$',
+                           message=_('Please enter the hexadecimal code of a color, e.g. #990000.')),
+            ColorContrastValidator()
+        ],
+        widget=forms.TextInput(attrs={'class': 'colorpickerfield'})
+    )
+    theme_color_danger = forms.CharField(
+        label=_("Accent color for errors"),
+        help_text=_("We strongly suggest to use a dark shade of red that has a good contrast for text on white "
+                    "ground."),
+        required=False,
+        validators=[
+            RegexValidator(regex='^#[0-9a-fA-F]{6}$',
+                           message=_('Please enter the hexadecimal code of a color, e.g. #990000.')),
+
+            ColorContrastValidator()
         ],
         widget=forms.TextInput(attrs={'class': 'colorpickerfield'})
     )

src/pretix/control/templates/pretixcontrol/event/display.html

@@ -20,8 +20,10 @@
         <fieldset>
             <legend>{% trans "Shop design" %}</legend>
             {% url "control:organizer.display" organizer=request.organizer.slug as org_url %}
-            {% propagated request.event org_url "primary_color" "primary_font" %}
+            {% propagated request.event org_url "primary_color" "primary_font" "theme_color_success" "theme_color_danger" %}
                 {% bootstrap_field form.primary_color layout="control" %}
+                {% bootstrap_field form.theme_color_success layout="control" %}
+                {% bootstrap_field form.theme_color_danger layout="control" %}
                 {% bootstrap_field form.primary_font layout="control" %}
             {% endpropagated %}
         </fieldset>

src/pretix/control/templates/pretixcontrol/organizers/display.html

@@ -23,6 +23,8 @@
                 {% endblocktrans %}
             </p>
             {% bootstrap_field form.primary_color layout="control" %}
+            {% bootstrap_field form.theme_color_success layout="control" %}
+            {% bootstrap_field form.theme_color_danger layout="control" %}
             {% bootstrap_field form.primary_font layout="control" %}
         </fieldset>
         <div class="form-group submit-group">

src/pretix/presale/style.py

@@ -40,6 +40,10 @@ def compile_scss(object, file="main.scss", fonts=True):
     sassrules = []
     if object.settings.get('primary_color'):
         sassrules.append('$brand-primary: {};'.format(object.settings.get('primary_color')))
+    if object.settings.get('theme_color_success'):
+        sassrules.append('$brand-success: {};'.format(object.settings.get('theme_color_success')))
+    if object.settings.get('theme_color_danger'):
+        sassrules.append('$brand-danger: {};'.format(object.settings.get('theme_color_danger')))
 
     font = object.settings.get('primary_font')
     if font != 'Open Sans' and fonts:

src/pretix/static/pretixbase/scss/_variables.scss

@@ -18,10 +18,10 @@ $text-color: #222222;
 $text-muted: #999999;
 
 $brand-primary: #7f5a91 !default;
-$brand-success: #50a167;
-$brand-info: #5f9cd4;
-$brand-warning: #ffb419;
-$brand-danger: #d36060;
+$brand-success: #50a167 !default;
+$brand-info: #5f9cd4 !default;
+$brand-warning: #ffb419 !default;
+$brand-danger: #d36060 !default;
 
 $btn-default-border: #CCCCCC;