They seem to have iridophores with the xanthophores, so they don't look that shiny yellow until light hits them. I collected 3 larvae, and they all have the same colouration. This one is the model simply because his fins are intact. The other two have imperfect fins, probably due to fish in the pond they came from.
Actually, if you have Petranka's Salamanders of the United States and Canada, he makes several references to specimens that were collected from the same pond as these guys back in the 1970s. These are the "large-bodied" Ambystoma mavortium mavortium he talks about a few times in the species account. They come from a population that was once largely neotenic, at least until a decade or so ago. I suspect these three will metamorphose though because there is a large population of goldfish in the pond now, as well as turtles, and I found no neotenic animals.