They would have to change color scarves. The robes are black though either with the Hogwarts crest or they sew on their house crest. Whoever said that they didn't mention scarves and ties in the book is wrong.
Seriously though. James Potter was a much better man than Severus Snape. Whereas James bullied Snape while they were kids and then grew out of it, Snape used his position of power at Hogwarts to bully children.