Here is (finally) my report for the Dark Grey Monkey!
I headed to the Deadmines by myself, where he was the only one of this color that I saw. The tame was pretty easy at my level. I'm going with human names, so I settled on Rocky for this guy.
While the model itself is just okay in my opinion, this particular color is my favorite of the bunch since its eyes are black and not quite so crazy-looking.
As with my spider Penny, I've taken Rocky to several places and done several things, including sitting around town:
Doing some battlegrounds, where his small size and dark coloration seemed to help him not get beat as much as my very purple, very obvious spider (which was nice!):
Here we are in Blackfathom Deeps, where I also sorta got a swimming shot, but it's super dark and not very helpful (sorry!):
The swimming animation isn't anything flashy or exciting, he just kinda swims like a humanoid.
Dance party!:
His combat animations boil down to various slaps and smacks:
His family ability, Primal Agility, is okay (increases dodge chance by 30%). For damage reduction it's not horrible, but the cooldown (2 minutes) on it is longer than other pets with damage-reducing abilities (like turtles with Shell Shield with a CD of 1 minute, for example). So again, it's okay, but nothing to write home about.
For the most part, monkeys are okay pets. Not great, not horrible. HOWEVER, their combat sounds are probably a deal breaker for me. The constant whooping and screeching was pretty irritating, and I was back in range. I honestly felt bad taking him into dungeons where my melee group members had to listen to that constantly. No one said anything, but I still felt bad about it. For that reason alone, I probably wouldn't use him in group content. Also, his running animation is a little strange, because his body is positioned diagonally but he runs in a straight line. It's really weird, but unfortunately I didn't think to get a picture of it.
Soooo, the verdict is that I probably won't use him after Dansen reaches max level. I left Rocky in my stable for now since I have tons of space, and I suppose I'll probably hang on to my challenge pets, but I'd definitely use Penny over Rocky any day.

However, if someone really wanted to tame a monkey, I
would recommend this color since I think it's the most natural, and the eyes won't give you nightmares.
Time for my next challenge pet!
(Excited because it feels like it's been a while.)
Name: Dansen
Level: 30
Exotics?: Yes
Restrictions: Pets between 21-30 please, and no mechanicals (still not ready for another spider or monkey yet, either)