Like PNA pointed out, Machine Grey is the closest color the Crossfire offered that comes close to being dark blue.
With the installation of a white top, it would suck the metallic right out of the paint, so it would probably look even more like dark blue.
Sounds like the OP has already made up his mind on the Miata, it's going to wind up costing him more money, but they still are great cars so good luck to him.