Wearing the blue shirt made a world of difference when flying night freight on a Metro. Loading an unloading was done by "Pilotpower". Dirt seemd to show much less on a blue shirt and one could wear it a bit longer than white shirt would have allowed.
Many schools in US had blue shirts, and apparently still have. Some schools force students to wear epaulettes/stripes anf if I remember correctly Sierra Academy had burgundy coloured stripes
I'd be much happier flying in T-shirt and Shorts, but a uniform makes life a lot easier, on most occasions, when going through security, immigration (USA excluded) customs etc.
AD