First,make a new image of any size (transparent image,you can make it transparent by selecting it in the advanced options.)
Then make any line or whatever of any colour like this :
http://i49.tinypic.com/2cief0y.jpg
And now copy the layer and make a new one,paste it in and drag the copied layer down below the first layer in the layer box.
Then go to colours at the top,brightness and contrast and make the brightness as low as possible and contrast as high as possible (uncheck the main layer which is red)
So you only see the one that you're making black and od that until it goes completely black.
http://i50.tinypic.com/6hmkcw.jpg
And then finally,check again the red layer and then g to the black line layer and blur it with gaussian blur,you go to filters and then blur,gaussian blur.The you have a cool shade behind the line
http://i50.tinypic.com/2a7exx1.jpg
Now use this on your heads,show me what you can do
Here is a head that I used the same effects on :
The names/terms are from GIMP but this can be done on Photoshop too : P