Was the yellow in green leaves there all along?
绿叶里的黄色，原来早就有了？
春天看树叶，我们常常先看到绿色。
When we look at leaves in spring, green is often the first color we notice.
可是到了秋天，有些叶子会变成黄色或橙色。
In autumn, however, some leaves become yellow or orange.
这些颜色是秋天才加进去的吗？
Are those colors only added in autumn?
不一定：叶子还是绿的时候，里面就可能已经有黄色和橙色的成分。
Not necessarily: yellow and orange pigments may already be present while the leaf is still green.
叶子里有一种叫叶绿素的东西，绿色主要来自它。
Leaves contain a substance called chlorophyll, which is the main source of their green color.
绿色很明显时，其他颜色就不容易看出来。
When green is prominent, the other colors are hard to see.
秋天白天变短，许多落叶树的叶子不再制造那么多叶绿素。
As autumn days shorten, the leaves of many deciduous trees no longer produce as much chlorophyll.
原来有的叶绿素也逐渐减少，绿色就没有那么明显了。
The chlorophyll already present also decreases gradually, making green less prominent.
这时，本来就在叶子里的黄色和橙色，就更容易被我们看见。
The yellow and orange already in the leaves then become easier for us to see.
不过，秋天的红叶不一定也是同一种情况。
Red autumn leaves, however, do not necessarily involve the same process.
有些叶子会在秋天形成新的红色成分。
Some leaves form new red pigments in autumn.
所以，叶子变色不一定是多了新颜色，也可能是原来的颜色终于显出来了。
A leaf changing color may therefore reveal an existing color, rather than add a new one.
