Store selected color scheme

app/controllers/preferences_controller.rb

@@ -21,7 +21,11 @@ def update
                                     else
                                       params[:user][:preferred_editor]
                                     end
-    if current_user.save
+
+    pref = current_user.preferences.find_or_create_by(:k => "site.color_scheme")
+    pref.v = params[:color_scheme]
+
+    if current_user.save && pref.save
       # Use a partial so that it is rendered during the next page load in the correct language.
       flash[:notice] = { :partial => "preferences/update_success_flash" }
       redirect_to preferences_path

test/controllers/preferences_controller_test.rb

@@ -51,4 +51,26 @@ def test_update_preferred_editor
     assert_select ".alert-success", /^Preferences updated/
     assert_select "dd", "Default (currently iD)"
   end
+
+  def test_update_preferred_site_color_scheme
+    user = create(:user, :languages => [])
+    session_for(user)
+    assert_nil user.preferences.find_by(:k => "site.color_scheme")
+
+    # Changing when previously not defined
+    put preferences_path, :params => { :user => user.attributes, :color_scheme => "light" }
+    assert_redirected_to preferences_path
+    follow_redirect!
+    assert_template :show
+    assert_select ".alert-success", /^Preferences updated/
+    assert_equal "light", user.preferences.find_by(:k => "site.color_scheme")&.v
+
+    # Changing when previously defined
+    put preferences_path, :params => { :user => user.attributes, :color_scheme => "auto" }
+    assert_redirected_to preferences_path
+    follow_redirect!
+    assert_template :show
+    assert_select ".alert-success", /^Preferences updated/
+    assert_equal "auto", user.preferences.find_by(:k => "site.color_scheme")&.v
+  end
 end