Damballah is generally called on for protection and to "cool" things (such as calming down a rival, etc.). He is served a white egg on a white plate of flour. When in possession, Damballah eats the egg without using any of his limbs like the Egg eating snake.
Damballah has a wife Ayido Wedo who is envisioned as a rainbow (depicted as a rainbow colored serpent). She is represented by Santa Dominidora while Damballah is syncretized with St. Patrick, though some say this is the Petro aspect and his Rada aspect is represented by Moses.
Damballah's color is of course white: pure white. It is extremely important that you keep anything "hot" or negative away from Damballah's altar and that it is very clean. Never let any food offering decompose on his altar either. He does not like those things very much. Damballah's day is of course St. Patrick's day and can be served on Thursday- the day for all of the Rada lwa.