And indeed, as Rashi pointed out, we learned that Joseph's coat of many colors was made from the fabric used at Ahasuerus's feast, which decorated the courtyard of the king's palace garden with "white, green, and blue hangings, fastened with cords of fine linen and purple" (Esther 1:6). This is also the reason for eating karpas (a vegetable, usually parsley or celery) at the Passover Seder, and we need to explain allegorically the connection between them. Additionally, in the Megillah itself, we need to understand what it teaches us for future generations that the place of Ahasuerus's feast was decorated with white, green, and blue hangings.