Gatsby's Pink Suit

I haven't read this novel in ages and I technically don't study it, but I am just going to take this as if it was an unseen paper and offer some suggestions.

For me, I would assume that the pink suit suggests that Gatsby is a flamboyant, excessive person (as evidenced by his never-ending crazy parties). A pink suit is a really loud outfit in general, and to wear something this loud, especially since he's a man, in an era just very recently out of the Victorian-Edwardian period of wearing black and conservative singles Gatsby out of his environment and demands attention. If you want to try, you can link this loudness (combined with his parties) as part of his strategy of trying to attract Daisy's attention.

As for it being un-Oxfordly...I can't be sure, but since Oxford is (presumably) the oldest English university in the world, it could symbolise tradition and order and 'properness'. So to juxtapose Oxford's traditional setting with Gatsby's non-traditional attire and behaviour, especially when worded in that way in that quote, implies that Tom doesn't exactly believe that such a man can come out of this kind of university.