What bugs me about Coby, even if I like him, is that he reacts like a little girl to his COO (yeah, like Aisa)...
Also, and correct me if i'm wrong, Haki means "willpower" or something alike. So the three colors are just 3 parts of a whole. And what's terrifying marines about luffy is that his raw power, revealed with Haoushoku, is huge.
Really? That's actually one of the scenes that really stood out for me and made me love him even more.
Coby standing up to Akainu proved how much more badass he had grown, that the little cabin boy that used to quake under Alvida's rule had matured into an upstanding Marine willing to take a stand and die in order to try and save the lives of all the Marines who were being needlessly sacrificed.
However, he's always had a kind heart and him crying over the fact that he can hear people's voices disappearing from his mind shows his empathy for others's suffering and how he hasn't lost his kindness or his morality. It shows how he's stayed the same, caring for others and not wanting to have any regrets.
Besides, he couldn't control his haki. Imagine, in the MIDDLE OF A WAR, with people dropping dead faster than flies, having an uncontrollable power that forces you to hear their cries disappearing one by one. I think that'd shake anyone up.
The reason I've always liked Coby so much is that he represents what I believe the Marines should be like. Dedicated to good rather than absolute Justice. I mean, even Smoker and Tashigi realized something was wrong, but Coby was the only one to speak up about it.
Personally, I salute him for his crazy suicidal courage and kind heart. <3