adhub

CF 7 uses same div to display error or success message. So it is no way to tell what color you need to apply. But ‘form’ tag that actually contains everything including message div changes some attribute to reflect submission status.

Example:

.wpcf7-response-output {
    color: green; //success
}

form.wpcf7-form[data-status='invalid'] .wpcf7-response-output {
    color: red; //error
}