social/website_mail_snippet_bg_color/views/assets.xml

<?xml version="1.0" encoding="utf-8"?>
<!-- © 2016 Antiun Ingeniería S.L. - Jairo Llopis
     License AGPL-3.0 or later (http://www.gnu.org/licenses/agpl.html). -->

<openerp>
<data>

<template id="assets_editor" inherit_id="website.assets_editor">
    <xpath expr=".">
        <script type="text/javascript"
                src="/website_mail_snippet_bg_color/static/src/js/bg_color_picker.js"/>
    </xpath>
</template>

</data>
</openerp>