See this site
http://www.bbc.co.uk/dna/h2g2/A839090 regarding the history of "Silver Arrows"
"Germany's motor-sport colour was white. At this time, as mentioned above, there was a maximum weight limit on the cars. Mercedes' car was weighed and found to be one kilo too heavy. Alfred Neubauer, the Mercedes team manager, hit upon the idea of stripping the paint from the cars. When combined with the filler (which smoothed the hand-beaten metal panels), this made up the necessary weight reduction. The cars were an instant success, and silver was quickly adopted as the German racing colour. Thus the dominant German cars of this period, the Mercedes and Auto Unions, were referred to as 'silver arrows', a name still occasionally applied to Mercedes DTM cars6 and McLaren-Mercedes F1 machines."