So if both the red and black are on the same breaker then putting the red on a second GFI isn't going to really help you unless you want that plug controlled by the switch. If you just want two GFI protected plugs outside your easiest route would be to put the black and white on the line side of a GFI and a normal plug coming off of the load side. You'll save the money for the second GFI and both plugs will still be protected.