This page describes how to use 是 properly in sentences:
是 (shì) is only used to link two nouns. It cannot be used to link a noun and an adjective. This is a very common mistake for people just beginning to learn Chinese. For that kind of sentence, you'll want to use a different structure with the linking word 很 (hěn).
It makes sense, but one pattern is not clear.
Take for example: "All her clothes are black."
Would you say, 她什麼衣服都很黑色,since you cannot say, 她什麼衣服都是黑色?
It seems strange to say 很黑色 in this context, so confirmation would be most appreciated.
It cannot be used to link a noun and an adjective.
This is incorrect; you can use 是, but there's a slightly different nuance if you do end up using it. For example,他臉**是**很紅啊~!His face **is** very red!
.他臉**確實是**紅哦!
or他臉**是**很紅哦!