I am assuming you are talking about dyeing his clothes as in the earlier Assassin's Creed games, and yes you can. There are certain outfits/armor that you cannot change the color of, like Master Assassin. Otherwise, change to your heart's content!
It was good. I didn't like it as much as Penumbra though (story was better). If you scare easily it will probably be more fun since Amnesia is scarier than Penumbra. It's not a very long game though, so don't go in expecting that, I got around 8-10 hours at most.
On this one I would recommend Relentless Assault, Diversity, and Combat Clinic. Those are the main ones I would consider using. Also main thing is to keep the fight as short as possible. There's a specific time when Doom is cast, after 20 minutes I think. Also unless you can't take the hit, keep attacking while he's building up for Destrudo, there's a chance of a... mini-stagger so to speak. He'll have to recharge and it weakens Destrudo. I like to use Tri-Disaster and Relentless Assault when he's charging for Destrudo. Hope this helps!
Yes, you can train in Revelations. I agree with slayer127, though, it felt a little lacking in this one, I really wasn't encouraged to train beyond the fact that I knew I should. The den defense also, although a great idea, left me wanting something a little bit more. Neither was enough to hurt the game though, in my opinion!
As far as I can tell, the bulk of the initial search is just that, searching. I usually climb all the way to the very top of every viewpoint, they love to stick them there! But after I believe about 50 or so, the rest show up as icons on your map. Until then, I'm thinking it's a whole lot of just exploring. Have fun hunting!