I need a white PSU with at least 500W. I'd like it to be modular if possible.
I don't think you'll find much.
If you can find one, the Fractal Design Tesla R2 650W comes in White. Right now they are out od stock at Newegg.
Look for a Super Flower Leadex Gold 550W in white!
Fully modular, excellent PSU.
https://www.amazon.com/gp/product/B0064XAJ30/ref=oh_aui_detailpage_o00_s00?ie=UTF8&psc=1 I bought one for 86.82