I just took a look at the one I had sorted in my Turkey collection. It's not anywhere as orange as the one shown in the pic above. It is more pale, more like yellow orange.
I remember reading somewhere that a few of the Turkish stamps were issued in different colors as revenues. Any possibility this might be one of them, Nigel (or anyone)?
I agree with you about the yellow orange shades. I think this is one is just darker than usual and/or maybe oxidised. I'll have another look at mine in natural light tomorrow.
I don't believe this is a revenue. The first Crete stamps were reissued in bistre-yellow as revenues but I don't remember Turkey doing this (although many of the early designs were also issued in black/brown/yellow brown colours as postage dues).