Turn signal colour
Soviet 1974 GAZ-24 Volga's taillight with red stop lamp, amber turn signal and white reversing lamp
Until the early 1960s, most front turn signals worldwide emitted white light and most rear turn signals emitted red. Amber front turn signals were voluntarily adopted by the auto industry in the USA for most vehicles beginning in the 1963 model year,[40][41] though the advent of amber signals was accompanied by legal stumbles in some states[42] and front turn signals were still legally permitted to emit white light until FMVSS 108 took effect for the 1968 model year, whereupon amber became the only permissible front turn signal colour. Presently, almost all countries outside North America require that all front, side and rear turn signals produce amber light. In North America the rear signals may be amber or red. American regulators and other proponents of red rear turn signals have historically asserted there is no proven safety benefit to amber signals, though it has been recognized since the 1960s that amber turn signals are more quickly spotted than red ones.[43][44][45] International proponents of amber rear signals say they are more easily discernible as turn signals,[46] and U.S. studies in the early 1990s demonstrated improvements in the speed and accuracy of following drivers' reaction to stop lamps when the turn signals were amber rather than red.[46][47][48][49][50] A 2008 U.S. study by the National Highway Traffic Safety Administration (NHTSA) suggests vehicles with amber rear signals rather than red ones are up to 28% less likely to be involved in certain kinds of collisions,[51] and a 2009 NHTSA study determined there is a significant overall safety benefit to amber rather than red rear turn signals.[52]
There is some evidence that turn signals with colourless clear lenses and amber bulbs may be less conspicuous in bright sunlight than those with amber lenses and colourless bulbs.[53]
http://en.wikipedia.org/wiki/Automotive_lighting#Rear_position_lamps_.28tail_lamps.29
