Never mind the colour, you should be looking at affordability and availability.
If this is state primary, them make it something that is sold in every supermarket, and available in different sizes and fabrics.
white polos
grey or black bottoms, of any description
keep it simple, affordable and practical.
white polos can be hot washed.
Coloured polos are not nearly as easy to find and they end up all being slightly different shades.
pe kits black shorts and white T shirts
No button shirts and no ties.
As for sweatshirts, make sure they are available locally and that there is a choice of sweatshirt and cardigan. If they must have a logo, make sure it isn't expensive.
after that - choose a colour! I think blue is good, I like navy. My kids had navy and it didn't really fade, they looked smart.
But an unusual colour can be cool, as long as it is available, there is a school near us that has purple, which looks really nice.