00 Scanning
I just scanned this ballpoint pen drawing in

01 Multiply
When arrived in Photoshop, I duplicated the layer and set the upper one to Multiply


02 Selection
Then I started to form a selection by using the lasso tool and filled it with a greyish brown


03 Coloring
A new layer was created to paint the color accents into the dull brown


04 Curves
By using curves I shifted the appearance of the creature into a more blue/violet direction

05 Gradient Map
And then there was this rainbow-like gradient map (20% opacity)