Open your photo and duplicate it
Add Hue / saturation from adjustment layer
Check Colorize option and drag the slider to the colour you want.
Select magnetic lasso tool
Make sure most of the dress is selected. You can always make adjustment later.
Select on the hue / saturation layer. Then from tool bar go to select > invers
Now select paint bucket tool and make sure the foreground colour is black.
Fill the image (outside the dress) you will see every thing other than the dress has gone back it its original colour. Basically we did a image mask.
The creator of this guide has not included tools
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