One reason is straightforward: on many trees, the leaves that are the reddest are those on the side of the tree which gets most sun.

有个原因很简单：在许多树上，最红的叶子是那些在树的一侧得到最多阳光的叶子。

youdao

The sun was beginning to set and sending deep gold-colored rays slanting under the trees when they parted.

太阳开始落山了，金色的光芒斜射进树底。两人就在这时分别了。

youdao

Oh, how peaceful it was with the little gnats dancing in the sun and the rustling of the trees!

啊，有小虫在阳光下跳舞，还有树木的沙沙声，多么宁静啊！

youdao

The sun rarely shines. The leaves on the trees are brown or have fallen to the ground.

VOA: special.2009.01.26

The sun slowly starts to slip behind the trees.

VOA: special.2009.08.19

Get lost on the roads that wind their way up and down the hills of the Black Forest, where the summer sun filters through the canopy of trees to dapple the road in front of you.

BBC: The classic Bavarian road trip

The mountains shimmer blue when the sun hits the eucalyptus vapors from the trees, at night, the dense star patterns of the Southern Hemisphere sky also shimmer in the clearest skies, and crossing the path to your cottage at night, you may well encounter a wombat, wallaby or kangaroo the 4000 acres are filled with them.

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These are the colors of nature, he elaborates, symbolizing the sun, trees, water and earth.

FORBES: Magazine Article