Sandwich Tern - leg color

In an interesting 4 September comment under the Sandwich Tern bill color discussion, Joseph Kennedy presents a photo of a juvenile Royal Tern with partly yellow-orange legs. Compared to one of his photos of juvenile Sandwich with yellow legs, the Royal appears to have brighter leg color. Presumably that is variable, but it would be interesting to compare a larger sample. I remember seeing a small but significant percentage of Royal Terns in fall at Cape May, NJ with partly to mostly yellow-orange legs. And non-black legs might be even more common, and more persistent, on Elegant Terns.