How can I change the post-submit "Thank You!" color in the newsletter form?

 Can I do it in settings or do I have to enter a code? I only found a way to change the color of the actual form font, but not the post-submit "thank you" that pops up. Any help appreciated.

You can use this code to Website > Website Tools > Custom CSS

div.form-submission-text {
    color: #f1f;
}