The phrase "You look like the fourth of July" is a colloquial way of saying that someone is looking particularly colorful, vibrant, and eye-catching. The phrase is often used to describe someone who is wearing bright, bold, and colorful clothing or accessories, or who has a radiant and lively appearance.
It could also be a compliment to someone who is looking especially patriotic or festive, as the Fourth of July is a national holiday in the United States, which is celebrated with parades, fireworks and patriotic ceremonies.
It's worth noting that the phrase is not meant to be taken literally, and is used as a way to express positive feelings towards the person's appearance.