On OLED screens dark mode does actually save power. My phone switches to dark mode when I turn on battery saving mode.
It probably doesn't matter much in the grand theme of this, but let's keep the criticism factual. God knows you don't need to make up arguments to criticize Nestle.
It only really does anything if the pixels can turn off completely. So the dark theme would have to feature full black backgrounds, not dark grey or anything like that.
But realistically, how much energy is really being saved on a global scale? If everyone who visited the nestle site all used dark mode, would it save more energy than a single car ride to work?
Definitely not nearly enough as if a company such as Nestlé acted to actually become sustainable and green, but it's all about guilt tripping John Smith into making his life more miserable on the fake promise that he's actually helping save the planet while companies keep trying to destroy it.
That's not true. You can go upwards to 33% grey and it'll have the same effect as completely black if I recall correctly, but the all around energy saved by using dark mode isn't anything to write home about, really.