Exchange my iphone for another with a different color

You could buy a phone case in the color you want.

How long have you had the phone?

I just got it today 

You can try returning it but there may be a restocking fee. Did you buy it from a store or on-line?

If you bought it on-line you will have to ship it back.

If you’re going to put a case on it, then the most cost-efficient way is what @syaoran suggested.

At the store 🫤

Take it back to the store to do the exchange. Like I stated earlier there may be a restocking fee and they may not have the color you want and will need to order.