social/website_mail_snippet_bg_color/views/snippets.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="email_designer_snippets"
          inherit_id="website_mail.email_designer_snippets">
    <xpath expr="//div[@id='snippet_options']">
        <div
            data-snippet-option-id='bg_color_picker'
            data-selector="[data-oe-field='body_html'] > *,
                           .bg_color_picker"
            data-selector-siblings="[data-oe-field='body_html'] > *"
            data-selector-children="[data-oe-field='body_html']">
            <li>
                <a href="#" class="button js_bg_color_picker">
                    Pick Background Color
                </a>
            </li>
        </div>
    </xpath>
</template>

</data>
</openerp>