Go to the settings page (/admin/setting)

Add a new setting: "feature.whitelabel.ios.use_theme" and set its value to true

Add a new setting: "feature.whitelabel.ios.theme" and set its value to a JSON object similar to below

{
  "Global" : {
		//color of foreground text
    "primaryForeground" : "#FFFFFF", 
		//color of header, "+" sign, icons at the bottom   
		"primaryColor" : "#000000", 
		//color of meta data
    "primaryFlatColor" : "#A4C785",
		//color of pull to refresh "loading" circle
    "tertiaryColor" : "#00BB00",
		//background color of question when viewing Q&A page
    "secondaryBackground" : "#F2F2F4",
		//background color of "Profile" header
    "primaryBackground" : "#00FF00",
		//background color of entire app
    "tertiaryBackground" : "#F6F6F8",
		//color of "Profile" and "My Activity" in the More tab
    "secondaryColor" : "#0A930A"
  }
}