The best way to do this is you have to cut out the dress.
Copy the picture and make a new layer for it.
Hide the background layer.
Now you have to isolate that dress. Use the magic wand, erasers, what ever you can to cut out that dress. (Sorry I did not do a good job I have a meeting at 3pm)
Use the colorize feature on the Hue/Sateration option and start changing the color.
Use blending options, smudge tools, and soft erasers to give it a finished look.
Another way is to select the dress with the quick selection tool (you can use refine edge to soften the edges of the selection) and then make a color fill layer using overlay, softlight, hue or color blend modes for the color fill layer.
Each blend mode gives a different tone (look) to the color. Then paint on the layer mask to refine the areas that the quick selection tool may have missed.