He was in a black mood.

他情绪不好。

I was feeling blue.

我心情不好。

There's no point in having these dark thoughts.

总想这些负面的事情没有意义。

His face darkened.

他的脸沉了下来。

They led a grey empty existence.

他们生存状况窘迫。

I'm afraid the outlook is very gloomy/bleak/dismal.

恐怕前景并不乐观。

The news cast a shadow over the evening.

那个消息让整个晚上都笼罩在阴霾中。