(something) is you
Something compliments or suits one well. Oh wow, that dress is you! That shade of green looks great against your skin. Oh, that painting is you—you have to get it.
it's you
Said when something compliments or suits one well. Oh wow, that dress, it's you! That shade of green looks great against your skin. A: "What do you think of this painting?" B: "Oh, it's you, for sure. It would look great with the rest of your décor."