Take a zone that is sure to be taken again soon, keep the app running (no GPS necessary, though), wait for the zone to be taken and then wait some more until it would have been revisitable if you'd still had it.

23 hours after I take a zone, there will sometimes appear a green blob over it, even if it isn't mine anymore. This will result in some conflicting colours. (I will post a picture soon). I think this only happens if I keep the app running the whole time but I'm not entirely sure.