Camouflage on RQ-4 Triton UAVs

White absorbs less energy. Black emits more.
The fast flying Backbird had to give away the maximum heat out of its red-hot skin (heatsink for air friction heat).
The slow flying Triton has to keep its cooling system less demanding hence absorb less energy from the surrounding elements (heat shielding from sun ray).

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I guess it is in a way – this is an aircraft which regularly and pretty much exclusively operates at 60k feet. At that kind of altitude, the sky above is very dark (almost black) while the background below is light, as the entire troposphere with all of its haze and clouds is lower. It could also be a thermal management measure, solar radiation is extremely intense up there (low density, no haze as mentioned) so painting the upper half white might help keep the equipment and avionics cool.