Phoenix Princess

Fire is a gradient, and that is the thing to work with here.

A flame is never one colour. It runs from white through yellow into orange and red and out to dark at the edges, and a phoenix design that uses only red is throwing away the most recognisable property the subject has. Build the gradient into the feathers, into the hem, into the hair, and the character starts to look like she is burning rather than like she is wearing red.

Gold is the other half of it, because metal is the only thing that reads as hot without being flame. Used sparingly it makes the reds look brighter.

From the Starsue monster princess set.