The idea of matt black bonnets on cars came about during the early 1970's for cars competing on the Safari Rally in Kenya. It was an answer to the problem of the sun reflecting off the more horizontal bonnets of cars from that period when driving thousands of miles through desert landscapes.
Modern cars tend to feature more sloping bonnets so this does not pose such a problem.
What is more amusing then VW Transporters with matt bonnets are chav-mobiles trying to look sporty with GLOSS black bonnets -no matter what colour the rest of the car is. They must have only picked up on the 'black' bit!