Yes it does refer to the colour of her wedding dress. Perhaps it is meant to show that they did have a traditional wedding despite their limited finances, or that she was a 'good' women (it has a symbolic meaning of purity), or that she got her wish - which was more the wedding than the marriage, or it could just be to show that they were a very conventional couple following the standard progression from courtship. I don't know, there could be lots of interpretations as to why the author made a point of mentioning it, but it is the colour of a traditional wedding dress in the UK.