It could be as simple as the differences in the ingredients between your salt mix and where they came from, or in water quality as a whole, or the lighting. It isn't terribly uncommon for zoas to morph slightly from tank to tank.
If they are truly 'extended' as in their 'stem' being more than 1/2" long, you may have them placed too low in the tank. If you chose to move them up, only do so in small increments of maybe 3" at a time.
They should not have to reach out to capture the light they want.
If at some point they start to take on an umbrella shape, then they are too high up.
Zoas do tend to pout a little when you move them, so do give them a couple of weeks (at least) to settle in if you plan to move them again after that.
Are you running carbon in the tank? Water tends to get a touch of yellow in it when you don't run carbon and that will also take away from their color visually.
The distance between your light & water is fine.