On each house perspective robe & sweater colours
(((THIS IS MY ASSUMPTION DONT TAKE IT SERIOUSLY))))
I think we can safely assume each house will have their own perspective color on their robe.
In the first picture, we could see a background character wearing what appears to be the distinctive green Slytherin robe, it looks fairly similar to the black robe displayed in the Licensing expo so i dont think it could be her personal clothing.
And the sweater itself will be universally burgundy, with accents of their house colors. I wish they would lean into actual Purple shades though instead of Burgundy, a purplish red color.
And from what i know purple is widely used as a general "magic" or neutral color in the wizarding world, ex: Albus Dumbledore robes, Wax seals in the acceptance letters, and wizard fashion. Its also Hogwarts unofficial school color i think.
I know we haven't seen much from the trailer alone but im looking forward to see other houses uniforms :))
Edit for more context: There is actually 2 distinct Robe color shown in the trailer itself & teaser pictures of the Golden trio which is Gryffindor personal color red & black in the trailer
Edit2: I guess i got it all wrong, their color are represented but in a different way. They will all have the same robe for each different occasions
burgundy outdoor robe to represent Gryffindor
Green snow robe to represent Slytherin
Yellow herbology robe to represent Hufflepuff
Ravenclaw is unknown