Pluto is not considered as a planet now. It's called a dwarf planet. And about the color, Pluto has a reddish brown color as per NASA articles. The reason behind this coloration is that the atmosphere of Pluto is covered with methane and the ultraviolet rays from the sun interact with this methane to give Pluto it's color.
Now your daughter can complete her project and you can give a perfect answer to her beautiful teacher.