I am looking for a way to implement a custom map style in iOS 7, just like you can do with Google Maps. I have found some posts saying that this is not possible with MapKit,
MKMapView does not expose the properties you're interested in customizing. The Google Maps SDK does support custom colors and icons for markers, which may be sufficient for your purposes.
Edit: Stay tuned for iOS 11, which may offer this level of customization.