He's mostly transparent; the shadow is somehow more substantial than he is.
I found some of these, dead, at Boundary Bay four years ago. This is the first live one I've seen. It was in a shallow tide pool where I was unsuccessfully trying to catch a sculpin. This little critter waltzed right into my collecting jar, and came home with me.
I wrote about these long ago, here (Part II of Muddy Buddies) and here (Part III).
Nebalia as I saw it and drew it, having no camera in those days.
It was a little harder to see this one, as I had to manipulate it very carefully, and it kept hiding in the sand. I couldn't get a microscope on it without hurting it, or breaking those almost invisible legs and tail.
If you look very closely, you can almost see the pointed tail of the carapace.
The whole carapace is transparent. This includes a separate, pointed rostrum over the head, and the long spine at the back. All the colour comes from the body of the animal underneath.
And a strange thing; all my dead samples had ruby red eyes; this guy's eyes are blue.