gnu-social/plugins/ProfileColor/templates/profileColor/profileColorView.html.twig

{% block stylesheets %}
    <style>
        #profile-{{ actor }} {
            background: {{ profile_color.background }} !important;
        }
        #profile-{{ actor }} * {
            color: {{ profile_color.color }} !important;
        }
    </style>
{% endblock stylesheets %}