Use the header background color for a site in the digest email.

app/mailers/user_notifications.rb

@@ -39,6 +39,7 @@ class UserNotifications < ActionMailer::Base
 
     @site_name = SiteSetting.title
 
+    @header_color = ColorScheme.hex_for_name('header_background')
     @last_seen_at = I18n.l(@user.last_seen_at || @user.created_at, format: :short)
 
     # A list of topics to show the user

app/models/color_scheme.rb

@@ -60,6 +60,10 @@ class ColorScheme < ActiveRecord::Base
     new_color_scheme
   end
 
+  def self.hex_for_name(name)
+    # Can't use `where` here because base doesn't allow it
+    (enabled || base).colors.find {|c| c.name == name }.try(:hex)
+  end
 
   def colors=(arr)
     @colors_by_name = nil

app/views/user_notifications/digest.html.erb

@@ -1,6 +1,6 @@
 <table style="border: 1px solid #ddd;" cellspacing="0" cellpadding="0">
 <tr>
-  <td style="padding: 10px 10px; background-color: #eee;">
+  <td style="padding: 10px 10px; background-color: #<%= @header_color %>;">
     <a href="<%= Discourse.base_url %>">
     <img src="<%= logo_url %>" style="max-height: 35px; min-height: 35px; height: 35px;" class='site-logo'></a>
   </td>

spec/models/color_scheme_spec.rb

@@ -40,6 +40,16 @@ describe ColorScheme do
       second.hex.should == base_colors[:second_one]
       third.hex.should == 'F00D33'
     end
+
+    context "hex_for_name without anything enabled" do
+      it "returns nil for a missing attribute" do
+        described_class.hex_for_name('undefined').should be_nil
+      end
+
+      it "returns the base color for an attribute" do
+        described_class.hex_for_name('second_one').should == base_colors[:second_one]
+      end
+    end
   end
 
   describe "destroy" do
@@ -59,8 +69,10 @@ describe ColorScheme do
     end
 
     it "returns the enabled color scheme" do
+      described_class.hex_for_name('$primary_background_color').should be_nil
       c = described_class.create(valid_params.merge(enabled: true))
       described_class.enabled.id.should == c.id
+      described_class.hex_for_name('$primary_background_color').should == "FFBB00"
     end
   end
 end