Purple is quite an elegant color. I prefer more of a royal purple which is darker, but I think it makes a good dress. I also like the peach and turquoise one. I would wear a white dress to the prom, though.
I think the peach and the turqoise one look really pretty. the purple one doesn't look like it'd flatter anyone's body...but it's your choice. good luck ^.^
Here are one dress with the similar color