how old is it??i would suggest giving it some time for the yellow to come in if it is selling as a sun. the yellow usually comes in at around 6months and all the way to about 2years for all the yellow settle in.
mine looked like this at about 5months old
but now at around 7months they look like this.
only time will tell if its a sun or how much ya trust the seller. but i will say that theres a high possibility that its a sun!!