Ghost dragons rarely make themselves visible, as to eat souls in peace. They are transparent white, with sometimes light pink and purple to go along with their "ghostly" colors.
The Traveling Writers Notes
Not much is known about the ghost dragon except that, when they wish, they can become nearly entirely transparent to normal untreated human eyes.
Side note: some believe that the ghost dragon devours souls, this is some of the best proof that many religions have that souls as well as their respective gods exist. it is unknown how these religions came to the conclusion that the ghost dragon has the ability to do this as there is no proof of anyone having died from this.