Nice complimentary colours, very clever idea too, although I'd have liked to see a more even spread of light, maybe lit from both sides to eradicate that dark shadow on the bottom left.
I like concept and result. I find the stronger shadow cast by the mask to make the photo somewhat unbalanced (but that just me, really). I wonder how it might look like with a refector lifting the shadow of the shell completely or even with a lighting setup so that the shell's shadow projects upward. That would make for an interesting oblique symmetry. But that's just me overthinking, good concept, well done!