Well, just to chime in again. Once the unit is running and pulling in air, there may not be a bunch of difference. But if the unit is cycling on and off, the white cover should keep the hardware temps down. So there should be some benefit initially. FWIW, for my mothers S&B AC unit, based on a write-up in the local paper, I built a white structure over her unit. During the afternoon it was in full sunlight. It seemed to help her - electric bill dropped a bit.
Flagstaff 26FKWS / 2016 F-150 3.5 EcoBoost SCrew