For this coloring page, I would start with coloring the trolls. I would use bright and vibrant colors, like pink, purple and orange, to make the trolls really stand out from the green of the background. Then, I would use lighter shades of the same colors on the trolls' clothing and hair. For the spikes on the big troll's back and the Mohawks, I would use a deep blue or red to make them really pop. I would use yellow to shade the noses and eyes of the trolls, and use black to outline them. Finally, I would use various shades of green, from bright to dark, to color the background and add some depth.