Step 1: open up your picture. color the background to any color you want. if you don’t know how, refer to this tutorial. (don’t add any coloring/psd first)

Step 2: Save the picture in step 1 and open the picture back in photoshop.

Step 3: duplicate the picture(layer>duplicate layer). select the magic wand tool and click on the background color on the picture. (x)

Step 4: your background color should be selected by now. right click on the picture and click select inverse. go to layer>new fill layer>solid color. choose any color you want for the shadow. 

Step 5: on the background copy layer, using the magic wand tool,select the background color.(the color you pick in step 1). right click>select inverse. 

Step 6: go to refine edge. something should pop up. change the output to: New layer. 

Step 7: another layer should appear in the layer tab. drag it to the top of all layer, like this.

Step 8: on the color fill layer, using the arrow tool. move the picture to the right or left. you’ll see shadow behind the person.

Step 9: Now add coloring/psd to the picture and edit it as usual. flatten the image if you’re done. 

my final result. (x)