When Zell first appears in FFVIII, he's sporting his Garden uniform. Zell shows his relaxed attitude by wearing his sleeves rolled up just above his elbows. His jacket is zipped, though, unlike Squall's and from the picture to the left, it looks like he's wearing a white collared shirt underneath. Garden uniform is standard, so I suppose the above is all he could do to make his uniform unique. :)

The SeeD uniform is what he wears after he graduates and...well, becomes a SeeD. This one hasn't been tampered with and he only wears it once during the game. It's a fancier outfit, trimmed in red and gold, and Zell seems very proud to be wearing it. I get the impression Zell likes clothes and fashion, as he never complains about wearing his student uniform and seems happy as a clam to have on the SeeD dress. (...Happy as a clam. :D)

This is the outfit Zell is seen in the most. The pants are loose fitting, and he's added a short jacket over his tight black shirt. He still wears his black gloves (which can now be upgraded) and also wears red shoes with gray socks. His jacket has a blue flame-like design on the sleeves, kind of similar to the tattoo on his face.