Which skirt is blue? X Which is skirt blue?

Fazendo exercicíos em um site a resposta correta é:
Which skirt is blue?
Mas o verbo "to be" não deve vir antes do sujeito ao fazer uma pergunta? No caso o sujeito seria "saia", correto? "is" não deveria vir antes de skirt ao fazer a pergunta?
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Avatar do usuário PPAULO 42175 6 33 742
Simple, it´s a Wh- question that involves the verb to be. So, a special case.
Well, in this case (of your sentence) you have "wich plus a noun", so after it you follow the pattern
Which / whose+ noun + main verb (that is the verb "to be" in your case).

1. We can use which or whose as the subject of the verb in the questions in these ways:

Which insurance company are you contacting tomorrow?[/i]
https://learningenglishgrammar.wordpres ... questions/

http://learnenglish.britishcouncil.org/ ... -negatives
Acho que entendi, mas se eu colocasse "which is skirt blue?" estaria incorreto?
Avatar do usuário PPAULO 42175 6 33 742
Would be wrong.

By the way, it would be a question in wich you usually had two options, you would have to pick one.
For example, if I am or another person is seeing two skirts, one green and one blue, chances are that I or the person asks you "which skirt is blue?"
If there were more alternatives, say, several skirts in several colours (and one blue among them), you problably would be asked the question "what skirt is blue?" -not "what is blue skirt?'' - agreed?

http://www.inglesnapontadalingua.com.br ... which.html

Notice that you (and others that are learning English) problably is used to the pattern of questions with "what + is", so you don´t feel anything weird about it. If you think of "which" as a cousin of "what" it can work as a mnemonics to memorize the pattern (I mean, a way to accept and remember how to use it on a regular basis).
I hope it helps.