Sorting Ceremony and Uniforms

[Donna]

If you take a really close look at the movie, you will see that the 
First years wear ties that are black with the Hogwarts crest on 
them.  It is the same tie that Madam Hooch wears.  They get their 
house colors in the next scene.  Watch as the camera pans to Harry in 
the window.  Look at the chairs.  Their scarves, ties and other items 
are placed on the chairs by their beds.

As to how they get their house patches on their uniforms and cloaks, 
while not shown in the movie, I like to think that the crests are 
sewn on by some very industrious house elves during their first night.

D