You should be looking for the meta-setting theme-color in the page's header, in my opinion.
<meta name="theme-color" content="#4285f4">
However, because it's an Apple product... You never really know if they adhere to the industry norm, don't you think? If that doesn't work, you could attempt the web-app-status-bar styling, but your colour options are quite limited—you can only use the default colours of black or black translucent.
<meta name="apple-mobile-web-app-status-bar-style" content="black">