I have been breeding rats for pets for ten years and there isn't a personality difference between coats. While most of my agoutis seem to be more active, none are more aggressive.

As for taming them down, I like to take one rat out (that I'm having problems with) every night while I'm watching TV or working on the computer. Just being on your lap and it not being a negative experience builds a lot of trust. Also, treats and physically dropping food in their enclosure (instead of a feeding hopper) also associates you with a pleasant thing. Speaking softly and handling gently (not using their tail as a handle) helps. Once they trust you enough that they don't run every time they see you, a light scratching on their behind and saying something in a playful voice lets them know that you are playing with them. Followed by making your hand scamper across their cage floor (like a rat running around), and they will chase it. They like foil balls and jingle balls, and watching you mess around with these things in their enclosure will build their interest in you and make them less afraid. You might also want to just stand there with your hand in their enclosure until they show interest in you. When they do, reward them by dropping a treat beside them.

Anyway, those are just a few ideas. Hope it helps.