Trying to get a certain effect - Need Help

[Mister Not So Technical]

I'm trying to figure out how to get a certain look on an image. See the attached photo. You'll notice the different colours ranging from the start to the finish. That is the effect I am looking for. Any help would be greatly appreciated.

[Ego Eram Reputo]

Off the top of my head, I'd try selecting just the lines in the drawing then applying a multi-color gradient.  How?

 

1.  Open the image and use this plugin (Isolate LineArt) to remove the background, leaving just transparency surrounding the lines.

 

2. Switch to the Magic Wand tool and dial the tolerance of the tool down to about 15%. 

 

3. Hold down the Shift key & click anywhere on the image that is not a line (i.e. we're selecting transparent background).  The Shift key toggles the selection mode to Global, so the selection is the matching pixels across the entire layer.

 

4. Invert the selection with Ctrl + I.  Now we have the lines selected.

 

5. Use this plugin Multi Color Gradient to recolor the lines.

 

Here's a quick demo of the technique.