wear a red coat（动词短语）例如：He often wears a red coat to school.
他常常穿一件红大衣去学校.
in a red coat （介词短语） 例如：The man in a red coat is from my hometown.
那个穿红大衣的男的来自于我的家乡.
He is in a red coat now.
他现在穿着一件红大衣.
be dressed in + 颜色、衣服（固定短语）
例如：
She was dressed in a red coat.
她穿一件红色的衣服