republic of china school uniform
The May Fourth outfit, or Republic of China era school uniform, consists of a black medium skirt and a blue shirt with a mandarin collar. It can be in other colors as well, but this is the most famous combination.
In the painting "May Fourth Movement" by Liang Yulong (梁玉龙) a woman can be seen in the front lines of a parade wearing this outfit, which is likely the origin of this particular color combination being the most popular.
Examples
This tag automatically adds school_uniform (learn more).