Among Yerushalmi Chareidim, a special dress code seems to have developed which has some features which are unique from standard Eastern Ashkenazi dress. While most Chareidim I have seen wear black coats or jackets, the Yerushalmim wear more colourful clothing: a blue-and-white striped kaftan on weekdays and a gold-and-blue one on Shabbat.*
What is the origin of the Yerushalmi kaftan and why is it colourful when most Chareidim are makpid on black or dark grey?
*Source, I have seen it in Me'ah Shearim and the Rova.