No. White Fusion, and white sprays in general cover dark plastic just fine. A lot of peeps use white Fusion as their primer. Just remember, multiple thin coats. Even if the first coat doesn't look like it's completely covered the dark plastic, let it cure and you'll get it on the second or third coat.
Thanks for the reply! I'm glad I can skip that step. Thanks for the reminder about multiple thin coats. I'm a first time customizer and I want to get it as good as I can!