Why is 这件衣服有点儿深颜色 grammatically wrong?
有点儿深 is used to modified 这件衣服颜色, it is appropriate to put modifier after somethings you want to modified. For example 這個音樂非常好聽 you will not say  這個非常好聽音樂. So I use bracket parentheses to denote this structure as [Somethings] [description used to modified somethings]. There are tones of example you can find.