Sorry Avshow but this is wrong.
The dot tells you the level of the monster.

Every map has a maximum and a minimum level.
Dead City 16-21, Kraken 21-26, Nordr 26-31 and Shuyal 30-36.

Only the maps where Bael || and Krunch || can spawn, can scale up to 36.
Do you guys never asked yourself why the monsters and Bosses in Windmoore Harbor, Skull Cove, Mt Spyr, (...), have a blue dot (if your are solo or everyone is on the same level or your are 36)? Because they'll scale to your level. And the maximum is 36.

Jurn Woods is grey because Bael or Krunch don't spawn there. The max level is 31. So if you are on level 36, the monsters will have a grey dot.

Grey = -4 levels or more
Green = I think -1 or -2 levels

But the Spiders in the Arena have a dark blue dot which means they are 1 level above yours. I'm 36.. And the spiders are 37?! How's that possible?