Styling UIDatePicker Programmatically

I have a register form which contains age, when a user enters their age a UIDatePicker will pop up and they can select a date. I am running the following code in the viewDidLoad to achieve this:

- (void)configureAgePicker {

    //Initialise date picker
    UIDatePicker *datePicker = [[UIDatePicker alloc] init];
    datePicker.datePickerMode = UIDatePickerModeDate;
    datePicker.locale = [[NSLocale alloc] initWithLocaleIdentifier:@"en_UK"];

    //Add toolbar to keyboard
    UIToolbar *toolBar=[[UIToolbar alloc]initWithFrame:CGRectMake(0, 0, self.view.frame.size.width, 44)];
    UIBarButtonItem *doneBtn=[[UIBarButtonItem alloc]initWithTitle:@"Done" style:UIBarButtonItemStylePlain target:self action:@selector(resignKeyboards)];
    UIBarButtonItem *space=[[UIBarButtonItem alloc]initWithBarButtonSystemItem:UIBarButtonSystemItemFlexibleSpace target:nil action:nil];
    [toolBar setItems:[NSArray arrayWithObjects:space,doneBtn, nil]];

    //style popup
    toolBar.barTintColor = kPrimaryHighlightGradient;
    datePicker.backgroundColor = kPrimaryHighlight;
    datePicker.tintColor = kTextColor4;

    self.ageTextfield.inputAccessoryView = toolBar;
    self.ageTextfield.inputView = datePicker;

}

My problem is that I cannot change the colour properties of the date picker itself. I can set the colour of the toolbar (that works fine) but datePicker.backgroundColor & datePicker.tintColor don't appear to be doing anything. Here is an image of the textfield,

I really want to change the colours of this popup to match the colour scheme of my app. I have styled UIDatePickers before through storyboards and remember having to use runtime variables to set the colour schemes (I couldn't through code). Since I am creating this date picker through code and adding it to the textfields keyboard, is there more I have to do to change the colour scheme?