I have no actual data to back this up, but I wanted to throw out a few discussion points. The air conditioning is more efficient at removing heat than the heater is at making heat, heat pump versus resistive heat technology. You and I live in an area where heat is needed more months and to a greater degree than cooling.
Based on that, my opinion is that black would more efficient on a year round basis. Of course that might be different in a place like southern Arizona. You also have to consider how much you are in the car and at what times. I don't drive many hours in the late day, so with overheat protection off, there are very few hours I would spend at peak cooling times in the car. I'm much more likely to fire up the car, like this morning, when it 13F/-10C.
I ended up turning cabin overheat, sumon standby, and sentry mode all off. With these on, the car would us 4-5 kWh in a day, so living in one of the more expensive states for electricity, ...feel sorry for those in Alaska and Hawaii, it would cost me $30 a month just to have my car sitting. I would be much more concerned about which of these features I need to leave on, or being slightly less agressive on the accelerator, then the color of the interior.
That said, I have the white interior and and very happy with it.