The reason that gliders look different is because there are different subspecies in different habitats over several countries in the wild. The majority of US gliders have come from one country so most are similar in features. However, even in US, you can get different sizes and some different physical characteristics as even in Indonesia/PNG ( where most of the USD gliders originated) there are diffent subspecies or origin specific types.
Here in Australia, we have several subspecies. The tiny, silver greys from Northern Territory, the longer tailed slightly bigger gliders from Queensland and the large, darker chunky ones from down south. I have seen some chocolate brown ones that came from wild stock in one part of Victoria. These are quite distinctive.
Main differnces between say my own gliders and the average US glider is size. 200g is not uncommon for weight though I had one female 350g ! Next is the ears and face..whilst the US gliders have curved ears and fine long faces, mine have short rounded faces with big round ears. Our tails are a lot fluffier as a rule too. Colouring is definitely different with mine being darker.
Here are two Australian glider (breviceps breviceps) -head shots. They are full sisters.