Thanks lorenzo, that's the one
And now that I look closer, Delphinus may be right... but if you look at the way the yellow meets the edge of the shell (and sort of overlays it, like an extended mantle would) I don't think so. I'll study the pic a little more later (though that won't exactly be definitive) but if you look at the second scallop on the bottom of the clam, you can see the edge of the shell peeking out from behind the mantle.
Edit: Still, you're probably right. I guess I'll just have to mention that I don't want a flat blue clam when I order one.