I had navy blue cockpit carpet. It can get a little warm, but not that bad. My main problem with it is that it shows every little spec of dirt or lint. Kinda like a dark vehicle, it looks great when spotless. But, it's difficult to keep that way.
I just switched to a new kind of PVC flooring called DECKadence and absolutely love the stuff. It's much more comfortable than carpet and hides dirt. It can also get rained on without the sopping mess.
Mine is the Marine Blue color which is more of a medium blue. They do have a navy blue, though.