Audemars Piguet Royal Oak Watch 37MM Yellow Gold 15550BA. 50 m (5 ATM). The Audemars Piguet Royal Oak blends contemporary elegance with a captivating color scheme of stainless yellow and blue. Its 37mm 18k yellow gold case features a sapphire crystal and caseback with anti-glare coating, a striking turquoise dial, and luminescent markers. This watch is driven by the self-winding 5900 calibre, ensuring a generous 60-hour power reserve.