I think it is safe to say that generally we associate the colour red with three things: passion, danger and blood. However, what is most important to "The Scarlet Ibis" is the last symbolism, which can also be said to symbolise death. Let us remind ourselves of the definition of symbolism before we go any further. A symbol is an object, person, animal or event that we often associate with other concepts, such as peace or freedom. When an author uses symbols in his work he or she is adding deeper levels of meaning.
Thus when we examine the short story, we see that repeated reference is made to the colour red. The tree is described as "bleeding" with its blossom. Doodle is born "red and shrivelled" and the scarlet ibis is of course red. Therefore the repeated references to red perhaps symbolise the death of Doodle and act as a kind of foreshadowing. Lastly, and perhaps most significantly, as it makes the link between the scarlet ibis and Doodle clear, note how Doodle's body is described:
He lay very awkwardly, with his head thrown far back, making his vermilion neck appear unusually long and slim.
Vermilion of course is a bright red colour and the description of Doodle links him in our mind with the description of the dead scarlet ibis, making it clear that the colour red symbolises death in this moving short story.
The color red is usually associated with death and a sense of foreboding.