Could you possibly explain what the light-grey and dark-grey listing is? As much detail as you can please, if it's not too much trouble.
Sure...
A "light grey" list would be a server that is closer to a whitelist than a blacklist/open. An example would be that you can join the server, but you cannot build anything at all until you are added to a membership database which then gives you permissions to build stuff. You might even also be locked away in a starting area, so you cannot even get out of a dimension/island.
A "dark grey" list would be a server that is closer to a blacklist/open than a whitelist. An example would be that you can join the server, build stuff, place blocks, and whatnot, but you can only use certain items (no buckets, no tnt, etc) until you have been around for a certain amount of time, or you are added to the membership list to get permissions to do that. Normally they don't lock you into an island, but they may have a "newbie dimension" where they keep new members before they have been around long enough to gain full membership.
And, often, servers are a mix between these, which is why "greylists" are so diverse, as opposed to the extremely binary whitelist/blacklist choice.