If it isn't black—i.e. you can see the panel glowing in a dark room—it's "grey". With the Kuros, it's actually a reddish-purple glow. Even the KRPs had an obvious glow compared to my CRTs when watching it at night.
But it's not grey enough to be distracted from. Like i said, it glows, but the light emitted is so low that it looks light black. The darkest scenes from the last harry potter plays easily on my 151. The darker the scene you can tell theres an glow, but it's very low and doesn't look grey at all.
Not everyone has that purple glow. And those that do, it can only be seen on a full black screen. Not with dynamic content which is how we watch movies. I had that purple glow (or maybe i thought i did) but for some reason it's gone. Now on a full black screen it's very very dim and uniform.