Yes - I would major on the use of the colour red in this excellent short story, and how specifically it creates a link between the scarlet ibis, Doodle, and death. From the beginning the colour red is used to effectively foreshadow the tragic end of the story, both with the "bleeding trees" and the physical description of Doodle when he is born. The incident of the scarlet ibis only cements the links between Doodle and this rare bird which leads the story to its sad conclusion.
I would actually stick to specifically using the color red because that one color is such a strong image throughout the story. I would show the parallels between the scarlet (red) ibis and Doodle in life and death. Bear in mind that a scarlet ibis was a very unusual and beautiful bird to see in their region of the world. This is similar to Doodle in that he was unusual and beautiful in his own way as well. He is like the ibis because he is always so out of place in comparison to what his brother deems normal. Doodle is upset by the bird's death because he can relate to the bird and he is almost fearful that the different things in his world will die, so he is doomed to die. Doodle gave us a sense that even he knew his own time was limited and that he had already been granted much more than anyone had expected. The ibis also resembled Doodle in death because his brother gets a vivid image of the way the dead bird looked when he sees his brother. Red comes into play here as well because Doodle has blood trickling from the corner of his mouth. Red can symbolize several things in this story. It can symbolize differences, death, and love. White is not prevalent enough in this story to use it in an essay successfully.
I think that the image of the color red is more supportive to your essay. In the begining, the narrator gives us an image that forshadows Doodle's destiny, and one of the images that he uses is the bleeding tree (red).