[11.0] It is required to specify color_field in options to make tags colored

In Odoo 11.0 we need to specify color_field option for many2many_tags widget to make tags colored.

Before Odoo 11.0

<field name="tag_ids"
       widget="many2many_tags"
       placeholder="Tags..."
       domain="[('model_id.model', '=', 'purchase.order')]"
       context="{'default_model': 'purchase.order'}"/>

After Odoo 11.0

<field name="tag_ids"
       options="{'color_field': 'color'}"
       widget="many2many_tags"
       placeholder="Tags..."
       domain="[('model_id.model', '=', 'purchase.order')]"
       context="{'default_model': 'purchase.order'}"/>