Oda intended the 3 admirals to have extremely difficult DF abilites and not something easy to extinguish.
Kuzan is ice. Looking closer, its more of a super condensed form of
dry ice which irl hurts if we hold in hand. Extremely lazy personality due to the cold air that circulates his body making him sleepy mostly.
Borsalino is light. Another element difficult to extinguish, that is, however you are Teach or simply know a form of haki. That alone is easier said than done. Borsalino seems to have the personality of a nomaad/caveman if you look good enough.
Sakazuki on the other hand... is definitely something hard to extinguish. Sakazuki's personality if im not mistaken could be the reason for his name "dog", tough like a boot camp instructor/full of energy like a red bull drink.
Blue (Ice) Pheasant
Yellow (light)Monkey
Red (??)Dog
*EDIT*
It definitely couldnt be blood, since that would be a big problem once english dubbed in the super far future. But I think you should all take a look at this
http://en.wikipedia.org/wiki/Red_mercury
If sakazuki is this element, he could be the strongest of the 3 admirals for sure. I will take my chances and gamble on
Mercury. This matches his strict personality, an element for bombs, and is red. Found in a thermometer