When Ronstadt mentions to him about the color coding of the robes, it actually reminds him of how Hogwarts has their students sorted into color-coded houses: red and gold, blue and bronze, yellow and black, and green and silver.

Harry then looks at the colors of his new school robes and see that it’s in silver and black, “It looks like I’m being sent to Aer et Calculum. Which house did they sent you to? This is reminding me of how my old school placed students into houses with specific colors assigned to them.”