Quick, what's the first thing that comes to your mind when you think of red? For many, the answer is, blood. When it's spilled, somebody is hurt, or even dead. Blood is scary, even horrifying. But, it can also be beautiful, as we see in "The Scarlet Ibis."
There is lots of red going on here. The ibis itself is red. The "bleeding tree" makes us think of red. The bush beneath which Doodle dies is red. When Doodle is born his body is "red." Then there's this line:
He had been bleeding from the mouth, and his neck and the front of his shirt were stained a brilliant red. (4.49)
This is disturbing. It means Doodle is dead. It means he died alone, suffering. But, it's also beautiful – probably not if we actually looked at it, but because of the word "brilliant." "Brilliant" is usually used in a positive way. Great ideas are brilliant. Bright colors and sparkling jewels are brilliant. The moon and the stars are brilliant. Blood on the neck and shirt of a young boy are not brilliant. In fact, without the word brilliant, it's completely horrible.
The word tricks us into visualizing a somewhat sanitized image. There is a conflict between what we know to be something horrible, something we probably would have trouble looking at, and the beautiful way its presented. Such effects often "wake-up" the viewer or reader. Since we are responding to the image on seemingly conflicting levels, we, simply, aren't bored.
For Brother, finding beauty in the image of Doodle's bloodstained neck and t-shirt is probably a kind of defense mechanism. The image is too horrible for him to look at it, so he finds beauty in it. After the ibis dies, Brother thinks:
Even death did not mar its grace, for it lay on the earth like a broken vase of red flowers, and we stood around it, awed by its beauty. (4.25)
In this case, Brother sees the ibis as he might a painting. It is dead, but beautiful. Since Brother isn't emotionally attached to the bird, he isn't finding beauty in order to cope. He's simply observing. He carries that image of beauty with him, and calls on it to help him face his brother's body. In the final lines of the story he visually transforms Doodle into a scarlet ibis; he transforms blood into red feathers.