Can i return just to get a different color?

Well depends on country, I'm in Australia and we have different laws etc as do Europe.

Just have to read the contract terms.

Unless the phone has a fault or major issue then they will not replace it because you want to change colour. Again it depends on the carrier, country and things like this. I do not think it will be swapped just as you changed your mind.

If you are within the return period for the place of purchase, then you should be able to get a refund and purchase another. Apple does not do exchanges or warranty replacements for different colors.

Depends on how long you've had it, what country you're in, from what store you bought it, and whether a carrier contract is involved.

Most places have full refund for "changing mind" - usually within 10-14 days, but not necessarily swapping for another color. That may require a "restocking fee", but policies vary.