Show Icon in Safari Pinned Tabs
Creating Pinned Tab Icons


  Pinned Sites allow your users to keep their favorite websites open,
  running, and easily accessible. You can set the icon that the user
  sees when they pin your site by providing a vector image.


Providing the Vector Image


  Use 100% black for all vectors with a transparent background in SVG
  format and add the following markup to all webpages that the icon
  should represent (replacing "website_icon" with your own file's name).


&lt;link rel="mask-icon" href="website_icon.svg" color="red"&gt;



  In the example, the color attribute sets the display color of the
  image. That attribute can specify a single color with a hexadecimal
  value (#990000), an RGB value (rgb(153, 0, 0)), or a recognized
  color-keyword, such as: red, lime, or navy.


So if Wix is not providing the option, you have to set it programmatically by editing your HTML code ;)

https://developer.apple.com/library/prerelease/ios/documentation/AppleApplications/Reference/SafariWebContent/pinnedTabs/pinnedTabs.html