Q:

An idiom or phrase that includes "white" and means optimism

In Arabic, we have a phrase for optimism that literally translates as:

white look

And look means outlook or attitude towards life. So someone who is optimistic is said to have a white look. Is there any similar saying or phrase in English?

A:

One can say "look on the bright side (of life)". It doesn't include the word "white", but there is a connection between "bright" and "white".
It is a verb phrase, and can be used as an imperative:

Look on the bright side! The company lost less money than last year.

or descriptively:

He always looks on the bright side of life. Even when he lost his job he treated it like an opportunity to set up a business.

It was famously used by Monty Python Always look on the bright side of life.
Another possibility is "He has a sunny outlook (on life)".
You should be careful of the risk of cliché. Expressions that are overused become tired and boring. It is hard to use "look on the bright side of life" without bringing the song to mind. Most of the use of "sunny outlook" in writing is when there is a literal use (talking about how the sun can actually change our mood). Writers avoid the cliché when there is no justification for it.

