Or Orange Yellow

The same year, the Federal Aviation Authority required that the boxes, which were never actually black, be painted orange or yellow to aid visibility.

同年，美国联邦航空管理局要求将这些实际上从未是黑色的盒子刷成橙色或黄色，以提高能见度。

What is still not fully understood, however, is why some trees resort to producing red pigments while others don't bother, and simply reveal their orange or yellow hues.

然而，至今仍不完全清楚，为什么有些树木倾向于制造红色素，而有些树木不去刻意制造色素，但还是会呈现出橙色或黄色。

This unmasking explains the autumn colours of yellow and orange, but not the brilliant reds and purples of trees such as the maple or sumac.

这一发现解释了秋天的颜色是黄色和橙色，而不是像枫树或漆树那样明亮的红色和紫色。