Like this:
1. Duplicate the shirt layer
2. make a selection of the shirt by using the magic wand and clicking on the
white area around the shirt
3. save the selection to a channel for future use, then Select>Deselect
4. select the bottom layer and add a color fill adjustment layer with black as the color
(Layer>New Fill Layer>Solid Color)
5. select the top shirt layer and go to Layer>Layer Style>Blending Options
6. move the right This Layer slider to the left just enough so see black around the shirt, the
hold down the Alt or Option key and click on the left part of the slider to split it and move
it all the way to the left
7. go to File>Scripts>Flatten All Layer Effects
8. go to Layer>Matting>Remove White Matte
(the image should turn black)
9. change the color fill layer to another color other than black
10. select the top shirt layer and load your saved selection from the
channel you saved earlier
(Ctrl or Cmd click on the channel in the channels panel to load the selection)
11. Go to Edit>Fill>Contents>White
12. Select>Deselect
13. turn off the visibility of the bottom two layers and File>Save As>PNG with
smallest file size
(click on the eye to the left of each layer thumbnail in the layers panel to turn
off the visibility)
