do turn signal lights have to be yellow
Automotive lighting The colour of light emitted by vehicle lights is largely standardised by longstanding convention. It was first codified in the 1949 Vienna Convention on Road Traffic and later specified in the 1968 United Nations Convention on Road Traffic.[5][6] With some regional exceptions, lamps facing rearward must emit red light, lamps facing sideward and all turn signals must emit amber light, while lamps facing frontward must emit white or selective yellow light. No other colours are permitted except on emergency vehicles.
School bus yellow The color was chosen because it attracts attention and is noticed quickly in peripheral vision, faster than any other color. Scientists describe this as follows: "Lateral peripheral vision for detecting yellows is 1.24 times greater than for red."[2]