Maybe it's just me being clueless, but why would dark colors use less energy than lighter colors? All colors are made up of the three primary colors. Regardless of the color, a color is still being produced. Why would one need more energy.
I believe a scientist would be able to explain it better, but black is the absence of light. It takes very little to no energy to create black in visible lightwave frequencies (mu). Whereas white is the existence of all colors within the color spectrum (Look at the cover to Pink Floyd's
Dark Side of the Moon to get a better idea of it), and as for some colors needing more energy I believe the hierarchy is as follows:
Red: Most (0.7 mu) --> Purple: Least (0.4 mu)
As for an artist's POV, black is fucking difficult to make while painting. It's essentially taking all the colors on the colors spectrum (Red, Yellow, Blue for simplicity sake), then mixing each individual color with their respective secondaries (Green, Purple, Orange) and then taking all three combinations of brown and mixing them to create black. To me, that never works out, and I rarely add yellow to the mixture. I also substitute orange for brown. Just for kicks.
However, as an artist, while painting, it's the complete opposite. White is fucking easy: just don't paint there. Whereas if you don't have black, making it is fucking difficult. That's why in a lot of my paintings when I do a Spacescape, I use a ton of Red, Blue, Purple, Brown and Green to make a near-perfect black. Yellow is useless in the equation, unless you truly want to add in all secondary colors for the perfect brown. But that's just me.