A little history can clear this up.
While the thread has become a debate about amber and yellow, I'm going to return to the original topic and simply refer to it as yellow.
Traffic lights at one time were only red and green and had no warning a red indication was coming.
Some areas developed to yellow while others simply had the red and green on at the same time briefly.
The yellow technically and legally has the same meaning as a green. You are allowed to enter the intersection during a yellow indication. However, with the addition of a yellow light to warn of the imminent red, you rarely have a valid excuse if you enter on red.
And if you have to speed up to make it you either were going too fast in the first place or were playing Pokémon and not paying attention.
And additionally, you officially enter the intersection when the front of your vehicle crosses the stop bar painted on the road.
So, the yellow is just and extension of the green that warns your right-of-way to pass the stop bar is ending.
