Verifique el tipo de mensajes Django
{% if messages %}
{% for message in messages %}
{% if message.tags == 'success'%}
<script>M.toast({html: "{{message}}", classes: 'green rounded', displayLength:2000});</script>
{% elif message.tags == 'info'%}
<script>M.toast({html: "{{message}}", classes: 'blue rounded', displayLength:2000});</script>
{% elif message.tags == 'warning'%}
<script>M.toast({html: "{{message}}", classes: 'orange rounded', displayLength:10000});</script>
{% elif message.tags == 'error'%}
<script>M.toast({html: "{{message}}", classes: 'red rounded', displayLength:10000});</script>
{% endif %}
{% endfor %}
{% endif %}
Hasan Osman