Eastern Tiger Swallowtail, dark form/morph

Hi again, it is mid-summer and still long hot and humid day, making plants grow well. We have a lot of nectar sources, mostly Butterfly Bushes and many other assorted perennials and annuals for the butterflies. We get different species as the spring turns to summer and fall. Now we are seeing the dark form or morph of the Eastern Tiger Swallowtail. At first glance experienced folk know something is very different and can ID this quickly. Novices think it is a Spicebush or Black Swallowtail for the most part. Last year I had quite a few varying from very dark to almost a translucent yellow. Here is a normal or yellow version and then three dark form for you to view. Thanks a lot for looking and have a great day, Denis