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.
North America
Europe, Middle East and Africa
Asia Pacific