Notice that the mask is not perfect,
you can spend more time tightening up the selected
areas but for our purposes, this is close enough.
Save the selection as a new channel in case you
need to go back and clean it up some more or if you
have to start over. (in the menu bar Selection>Save
Now its time to change the color of the sweater.
Zoom out to view the whole image. With the sweater
still selected open the "Hue and Saturation" panel
(Ctrl-U or Image>Adjustments>Hue and Saturation).
Select the check box for "Colorize"