Sites like that might start to save energy again when LCD’s using adaptive backlit LED segments become commonplace, otherwise I think it wasn’t meant to be taken fully seriously but more a “what if” concept.
CRT’s I’m sure most know fire energy at glowy stuff. Black = Off.
With an LCD the pixel “on” state is “filter all light,” or, Black = On.
So in some situations blackle will consume more energy!
If you’re that worried there’s plently of ways to make your PC use less energy that don’t give up readablity, functionality, or bump up counters with questionable formulas 