girls in blue这个短语乍一看是穿蓝色衣服的女孩们，然而真实意思指女警察female police officers，这是由她们的警察制服延伸而来的表达，不要理解错了。

例句：

I brought my daughter to the police station so she could meet some girls in blue.

我带女儿去了警局，所以她能见到一些女警。