您必须访问UITextFieldUISearchBar内部。您可以通过使用valueForKey("searchField")

var textFieldInsideSearchBar = yourSearchbar.valueForKey("searchField") as? UITextField

textFieldInsideSearchBar?.textColor = yourcolor

Swift 3更新

let textFieldInsideSearchBar = yourSearchbar.value(forKey: "searchField") as? UITextField

textFieldInsideSearchBar?.textColor = yourcolor