Q. Why is the car's tail light red?

This has more to do with the psychological effect of light and the physics of light. Psychologically red is a colour associated with danger therefore whenever the car hits its brakes the tail lamp glows bright red. But more on the science behind it red light scatters the least amongst all the colours of VIBGYOR. Therefore this means that amongst all the colours of light Red will travel a further distance. So it is going to be visible to other drivers and cars located much further away. This enables the safety of both the car passengers to be aware that there are other cars in the vicinity. This comes in particularly handy during foggy and heavy rainy days.