White night — ночь без сна
He was hardly able to work after a few white nights.

Look blue — иметь унылый вид
Do you not why he look blue?

To sail under false colours — обманывать, лицемерить
Although he assured us of his support but he actually sailed under false colours.

Once in a blue moon — очень редко
Once in a blue moon we decided to go on vacation abroad but his leave was cancelled.

Out of the blue — совершенно неожиданно, как гром среди ясного неба
He lost his job out of the blue.

To look through blue glasses — смотреть мрачно, пессимистически
Her mother looked through blue glasses at her career.

Green hand — новичок, неопытный человек
It is not a job to be handled by a green hand.

Catch (someone) red-handed — поймать (кого-то) с поличным
The children were caught red-handed in the garden trying to steal apples.

White elephant — бесполезное приобретение
The new bookkeeping program was a white elephant and nobody wanted to us.