[jwilco]

In the UK they are white at the front and yellow at the rear. This is to help drivers on dark nights identify if the car in front is facing them or not.

(In Germany they are white at both ends of the car and in the Netherlands they are both yellow)

I imagine it's actually to help more during the day rather than at night. At night the white vs red lights will be a better visual indicator.

 

[jwilco]

The design was for when cars were parked in the dark and there were no streetlights I was told. (no red or white lights then)

There is also a rule that you must not show a red light at the front of the vehicle or a white at the rear except when reversing.

(KITT would not pass a UK MOT)

Just trying to think why it matters which direction a parked car is facing.