photoshop colouring in technique

I wanted to know how to change colour of an object in photoshop, make it colourful and I found a good tutorial explaining it, here it is:

This is what I've done for a practise. I'm a genius :D 
stage 1: the orginal smoke

 stage 2: rainbow effect

 stage 3: overlaying the layer

 stage 4 (optional): duplicating the layer