Firstly, you get access to speeders at lv25, but you can't just buy one and go for it, you actually have to buy a speeder riding ability from your skill trainer which costs 25,000 credits... and then on top of that the cheapest speeder costs 8,000. I think there are 2 or 3 choices for lv25 speeders which allow you to travel 90% faster than your regular run speed on foot.
There are higher level speeders which you can only use if you're the same level or higher. Some of these higher level speeders just look cooler, but others are actually faster than lower level ones. I think the three speeds of speeders so far are 90% faster, 100% faster and 110% faster.
As for colours, they're pretty limited, I think two of the lv25 speeders are the same with different paint schemes but they don't look all that good to be honest lol. But whatever, I got the CE version of TOR which comes with a free speeder so at the very least I don't have to waste 8,000 credits early on on a speeder.