Rose flowers changing colour

My non-gardening neighbour has a very large bush rose/hybrid rose in his back garden that's been there for over 25 years and was there when he bought the house
Early each year it has red flowers but later on in the year the flowers are yellow
He says these flowers are all over, so it's not another type grafted on
So why do the flowers change colour each year?

 

Sounds as though it could be " Masquerade " , but as far as i know this happens all the time . @wiseowl should be able to help.