[FIX] website: properly mark selected color for menu, footer, etc

When a color combination was used as "color" (base case) for the menu,
the menu background in the boxed template, the footer or the copyright
section, it was not properly marked as selected in the color palette
widget of the editor panel.

Related to task-2599770

closes odoo/odoo#75132

Signed-off-by: Quentin Smetz (qsm) <qsm@odoo.com>