Now, what we know about admirals so far is:
Akainu has absolute justice. He has his ideals, and he wants to impose them on the world - by force if necessary. He wants to destroy all the pirates, and may be willing to even go against the Gorosei if they contradict his idea of justice. His absolute justice dictates that evil has to be eradicated in its roots. This passionate view easily fits the color red and the fact that his element is magma: hot and destructive.
Kizaru has unclear justice. What this means is shown in newest chapters: guy simply doesn't give a crap. He does what he is told and that is it. He is lazy yet also thorough in dealing with pirates. Color yelow and element of light may seem to contradict this, but I don't think so. Light has no weight, yet can push. It is energy yet can behave as a wave and as a particle both. It can reveal things hidden by darkness, yet can also blind you if you look at it directly. This may imply that Kizaru in fact has some internal conflicts with regard to justice, that he doesn't yet know who he is, and solves this conflict by delegating morality to a higher authority.
Aokiji is lazy justice. He does not heavily pursue enforcing justice, and is willing to "live and let live" as long as something egregious isn't happening.
Ryokugyu I would say is in between Akainu and Kizaru. Like Akainu, he believes in absolute morality of the world government and necessity for thoroughness in dealing with pirates. But much like Kizaru, he has essentially delegated his own sense of morality to a higher authority: he is Akainu fanboy and believes in the natural superiority of Celestial Dragons. Yet he himself is green. What is up with that?