There is a long history of "dual pricing" in Turkey when it comes a yabanci, especially in bars & restaurants and anything to do with property maintenance such as plumbing, electrics, building work etc. But the term "yabanci" doesn't mean just foreigners, it also means stranger or outsider. In its literal meaning it could be someone from the next village or town, you don't have to just be a foreigner to classify as a yabanci.
I really don't have that much of an issue with it, it's just the way it is - if we eat out with (local Turkish) friends in a good few places Fethiye I know the bill will be lesser than if we were in the same place with (Turkish) friends from Istanbul.
Conversely, there are a number of places we use in Istanbul where we get a decent discount on the bill - someone from Fethiye would pay more, even if they were Turkish.
Swings and roundabouts for us methinks.
Even Spain has its own way of keeping locals happy - little things like not charging for bread, sending over a "special tapa" to try, free bottles of mixers and the absolute killer in a few bars, once you've settled the bill they send out a last round of drinks on the house
The Mulberry Tree isn't doing anything a Turkish restaurant wouldn't do - what makes it so wrong is that it is run by a British person, and their British customers probably take it on trust that everyone pays the same price. Personally I think they've been pretty stupid - give a discount yes, but to blatantly have different menus? The "waiting for new menus to arrive" excuse doesn't wash - from experience, getting printing work done in Turkey is always pretty quick and a heck of a lot cheaper than in the UK!
JF