Red coloration in apples
Many apple varieties have a the potential for an orange or red colouration. This can be noticeable as the fruitlets form in late spring. However the final extent of the varietal predisposition is heavily influenced by the level of autumn sunlight on the ripening fruit.
The following photographs are of a mature Red Falstaff tree growing on M9 rootstock. Both photos were taken at the same time, at midday in early October, and both photos are of the same tree. The only difference between the photos is that one was taken from the south-side of the tree - which gets the full effect of the autumn sunlight - whilst the other is taken from the north-side of the tree. At this time of year at this latitude (central England) the north-side of the tree gets very little direct sunlight as the sun is much lower in the sky even at midday than it was at mid-summer.
Red Falstaff tree, view from the north
Red Falstaff tree, view from the south
The red coloration can be brought out even in normally green apples by a combination of strong autumn sunlight and cold nights. We have seen orange-flushed Granny Smiths grown in the hills of the Limousin region of France - the relative altitude and clear cold air rendering the apples almost unsaleable as their trademark bright green was lost!