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Red means "stop," green means "go," and yellow means "hurry up and make that damn light." Why those colors, though? Why not blue, purple, and brown? I have to admit that aside from a hunch that it had to do with wavelengths, I had no idea myself, so I decided to look into it. 红灯“停”，绿灯“行”，黄灯亮了“快点走”，但为什么交通信号灯要用这三个颜色，而不用蓝色、紫色或者褐色呢？必须承认除了直觉认为这与波长有关外，我完全不知道原因，所以我决定一探究竟。 The answer, as it turns out, is a little convoluted, but makes sense. The earliest traffic signals were designed for trains, not cars. They were red and green, gas-powered, and more than a little dangerous in the event of a leak. 事实证明，答案确实有点复杂，不过倒也还讲得通。最早的交通信号灯是为火车而不是汽车通行设计。信号灯为红色和绿色，使用煤气，在漏油时会非常危险。 | 
