A Weird One

So I went out into the garden with the camera today to look for butterflies, and there in front of me on the deck was this one:

It is clearly a female Eastern Tiger Swallowtail, but the color pattern is off. As you may (or may not) know, females Eastern Tigers come in two morphs, a yellow morph, like all the males, except for the blue field on the hind wings:

and the black, or dark morph, thought to be mimic of the poisonous and inedible Pipevine Swallowtail:

But this one seems to be splitting the difference. Much lighter than the black morph, it's like a yellow morph covered in soot, and with a wedge of darkness from the top of the wing to the tail: