An adult orange tail is in the 280-375 range. Juvi's are less as quoted above, but extremely hard to know if it is a true orange tail unless you can confirm/trust the origin. As for color, indo has a yellow tail vs. the orange tail. The orange tail also has slightly more vibrant colors throughout the body too. Traditionally, most orange tails have come out of the Red Sea - hence the higher price tag.
Recently, I've seen a lot of indo's being sold as orange tail, so beware. You should see a distinct color variation - not subtle.