This site tells me:
It is illegal not to carry some form of photographic ID in Turkey. Carry a photocopy of your passport with you at all times.
However i want to double check. While it would be nice to only carry a copy of my passport, I'ld rather be sure. I have been getting International SOS Security Advisories emails (part of the International SOS service contract my employer has, i think), which say:
Expect increased security measures in areas affected by security force operations. Monitor local developments and allow extra time for journeys, carrying relevant identification to ease passage through security checkpoints and comply with all security force directives.
So I guess it is actually quiet likely that my ID will be checked at some point.
So is it true that I can use a photocopy of my passport? I have 3 in good color.