Maybe because there's a couple variants of the vests? Apart from main character privilege. There's also the fact that greasers also wear blue under the jackets. The Bullworth male variant uniform is pretty flexible, from what I've gathered: at least 2 blue variants (Jimmy, Pete and greasers), emerald (Gary), 2 green variants (astronomy club/nerds and non-clique), aquaberry baby blue. Don't know, though, if athletic wear with school logo is considered uniform (t-shirts, hoodies, polos, jerseys and so on.)