I unlock my phone, see the grey icons and don't feel the urge to dive in, I just do what I need and get out without flicking between apps.
I've seen comments that making this change renders the phone "unpalatable" but isn't that kind of the point? It may seem like a bit of a waste of the amazing display but what price sanity?
I don't know if the greyscale thing is actually working or if it's just psychological - perhaps because I know that the phone is supposed to be less enticing I am subconsciously convincing myself that's the case.
I think it's way too early to tell - it probably needs a while to get over the novelty of the situation before I really know if any change in behaviour is genuine or self-induced.
Still, whatever the reason, if it achieves the intended result isn't that all that matters?