"Je to šedá myš."

Translation: It is a gray mouse.

[Goran12]

"Šedá myš" may refer to the animal, but more likely it's an idiom for a shy person. I'm not sure which idioms would suit in English ("a grey mouse" doesn't seem to fit), but the idiomatic translation should definitely be preferred.

[standelf]

In English there is something rather similar: "as quiet as a mouse". It refers mostly to someone being very quiet and meek, not necessarily shy.

[ion1122]

If talking about a person, would you say "je to", or just "je"?

[VladaFu]

Depends on the context, both are possible. It does not really matter if it is a person or some other object. The usual rules apply.

[Tsubasanut]

Interesting. In russian same sentence means "a very not-standing-out person". Usually in both character and appearance, but more of the former. And applies only to women, cause myš is feminine. Strange to see notion difference in very similar languages.

[VladaFu]

Actually, I would be inclined for your definition even in Czech.

[TatjanaVol5]

Why not That mouse is gray?

[VladaFu]

That is: Ta myš je šedá.

[TatjanaVol5]

Many thanks.