When powdery mildew is rubbed, much of it rubs off. If it doesn't rub off, it's not powdery mildew. Powdery mildew spreads. Variegated patterns don't. Variegated patterns mostly follow the veins. Much as what I see here. Powdery mildew is in splotches.

Those are natural markings. Do what Dan says and you’ll find they don’t rub off. One other tip. Mildew smells mushroomy if you get your nose up close.

Mine all look like this. I'm pretty sure it's just varigation.

Thanks all! I'm relieved. Haven't grown Golden before so didn't know it had these types of leaves. I had powdery mildew on my zucchini last year but it was much later in the season, so this was stumping me. I'll leaf (ha) it alone then.