The black bits are used to cover up features, I believe, the blue covering is just to protect new cars as they are testing them.

Most at I see aren't covered, lot are blue, when you see black you know it's a bit special.

having said that, the pre pre production cars had big numbers on the side - one had a single exhaust a la P1 and the second had two exhausts A la 12C/ 650S it was obvious they were test cars but we had no idea at the time what they would release!