My Cruze was Black in Black. On Winter afternoons I frequently had to run the A/C. My Volt is Black in Silver/Gray and the Clarity is Tan in Green. I have to run the heat in these two cars in the same conditions where the Cruze was running the A/C. The Clarity needs the heat more often than the Volt - black seats capture heat. Basically, black interiors shift the heat vs. A/C point to lower external temperatures and adding a black exterior shifts it even more.
The other thing to remember is in the morning when it's coldest you haven't had the benefit of solar heating of the cabin, so the car's exterior and interior colors don't matter in this scenario.
As for which is more efficient, heat pumps are more efficient than resistive heat. Air Conditioning is always a heat pump, just pumping in the opposite direction.
I have seen various studies done regarding differences in exterior color which indicate about a ten degree difference in interior temperature during summer between white and black cars, and an estimated 0.5 mpg difference in fuel economy. That is less than the mpg difference between different types of tires. So while the effect is there it doesn't seem to be major, or similar to the case of tires not something that should be an overriding factor in a purchase decision. That being said my previous three cars were white specifically because I wanted to reduce the temperature during summer, and since white is among my favorite colors it was an easy choice for me. But if someone likes how black looks, or in the case of Clarity there are "styling" advantages to black, I don't think it should hold anyone back as the difference in mpg or EV range should be minor.
Back to my question of any advantage during winter, of course for an ICE car winter is a moot point since you normally have plenty of waste heat from the engine available. So it is understandable that I haven't seen any studies yet showing efficiency differences during winter with different car colors.
But with EV's there would be a difference, I just haven't seen any studies quantifying it yet. But if it is anything like a ten degree difference in winter that would be significant, especially for cars like Clarity that don't have a heat pump and instead use resistance heat which as I said is less efficient than a heat pump. However during winter the sun is at a lower angle, and there may be more cloudy days depending on location, so the average interior temperature difference might be less than ten degrees. But still heater efficiency being more of an issue for Clarity in winter than AC usage in summer, I would take a guess that it works out to a similar 0.5 mpg advantage in winter for Clarity by having a black exterior. If it is less than a 0.5 mpg gain during winter then at least it somewhat offsets the estimated 0.5 mpg loss during summer, making it even less of an issue.
Of course the actual comparison value would be MPGe but I used mpg for this discussion just because that is what is reported in studies that I have seen about summer efficiency differences.
You hardly see the fender skirts unless you are looking for them. And it eliminates the floating front bumper effect. And it pretty much hides the air scoops on the side. 
