This is because their colors are not bright enough to be noticed by the human eye.

这是因为它们的颜色不够明亮，无法被人眼注意到。

youdao

Is it too bright or not bright enough?

是太亮还是不够亮呢？

youdao

He is not bright, but he always works hard.

他并不聪明，但工作总是勤勤恳恳。

youdao

But the sun's bright reflection on the snow was blinding and he could not see his notes.

VOA: special.2011.04.10

The reason being, again, computers are not very bright.

你们也知道的，电脑很笨的。

哈佛公开课 - 计算机科学课程节选

I try to look on the bright side. I try to not be a downer.

我试着乐观一点。试着不去做一个扫兴的人。

幸福的定义 - SpeakingMax英语口语达人

Pistachios are not actually electric green, and neither are kiwis, while cantaloupes are light orange, not bright orange.

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Circuit City has been struggling to turn a profit for the past year and a half, and if history is any guide, the future for Circuit City is not bright.

FORBES: Magazine Article

One who tried to do so late last year, a bright reformer called Koichi Kato, proved not bright enough to carry his erstwhile supporters with him, and is now in the political wilderness.

ECONOMIST: Why Japan��s Mori must go