I think McL have agreed with Merc that McL will be shiny/bright silver while Merc is more matt – I guess that that works historically as the story is that the silver Merc colour originally came from a time when they stripped all the paint off their cars to save weight leaving aluminium which would be dull silver.
http://en.wikipedia.org/wiki/Silver_Arrows
A story exists that the origin of the Silver Arrows was accidental. The international governing body of motor sport prescribed for 1934 onwards a maximum weight limit of 750 kilograms for Grand Prix racing cars, excluding tyres and fuel. It is said that when in spring 1934 the Mercedes-Benz team placed its new Mercedes-Benz W25 on the scrutineering scales prior to the Eifelrennen at the Nürburgring, it allegedly recorded 751 kg (1,656 lb). Racing manager Alfred Neubauer and his driver Manfred von Brauchitsch, who both later published their memoires, claimed that they had the idea of scraping all the white paint from the bodywork. The story continues that the next day the shining silver aluminium beneath was exposed and scrutineering was passed. After the 350 hp (260 kW) car of v. Brauchitsch won the race, the nickname Silver Arrow was born, according to the legend.
[edit] Weight story disputed
This story did not appear until Alfred Neubauer’s biography was published in 1958, and no reference to it has been found in contemporary sources. It since has been established that von Brauchitsch in 1932 had raced a streamlined SSKL on the AVUS which was called Silver Arrow in live radio coverage. Also, in 1934, both Mercedes and Auto Union had entered the Avusrennen, but the Mercedes cars were not able to start, and Auto Union did not succeed either. The next big event was the Eifelrennen, but as few cars complying to the new rules were ready, it was held for Formule Libre, so weight was no issue at that time.[1]