Minecraft wiki entry for Wolf, associated text: Untamed wolves have gray fur, a drooping tail, and their eyes consist of a white pixel and a black pixel for the pupil (on each side). They are neutral toward the player and hostile toward sheep, rabbits, foxes, baby turtles, and skeletons. They avoid llamas, although wolves may attack a llama that spits on them. They do not despawn, even if they are in an unloaded chunk, or 32 blocks away from the player.
Angry wolves are characterized by their constant growling and fearsome appearance. Wild wolves become hostile when they are either attacked by a player or mob, if not killed in one hit‌[JE only], or when they see a mob they want to eat. Their tail is held out straight, their eyes become blood red, their mouth is raised in a slight snarl, and they have angry eyebrows. Angry wolves are hostile only to mobs that attack them, or to the mobs they are hunting. They can see attackers even if they are under the invisibility effect, but they cannot track the attacker down, if they get out of their render distance, or the attacker was able to unload the chunk where the wolves were. Angry wolves cannot be leashed, but a wild wolf may become angry while it is still leashed without dropping the lead.
Tamed wolves have friendlier looking eyes. They have a default red collar around their neck, which can be dyed using any color of dye on the wolf. This also includes other wolves owned by other player, where any player can dye that wolf's collar. Pressing use on the wolf makes it sit and remain in place and not follow the player around. Tamed wolves that are not sitting attack players or mobs that their owner attacks, or those that injure their owner unless the target has the same owner or is on the same team. They do not attack creepers, ghasts, tamed horses or tamed cats, regardless of owner. Standing tamed wolves attack only skeletons and their variants without provocation. Tamed wolves are always passive to the player, even if the player hits them or kills a tamed wolf on the same team.