The three tanks in this coloring page are metal behemoths lined up one after the other. The bulk of metal is imposing and glints in the sunlight. Each tank is equipped with treads along the underside that make them powerful, mobile war machines. All of them have big guns placed on their fronts, ready for battle. As for the color, each tank is a deep, forest green, a hue that captures the power and scale of the vehicles.
To get the most out of this picture, I would start by blocking in the primary green color with a light shade of the same hue. Then I would add in a bit of shading, maybe some greyish-brown tones that bring out different aspects of the metal. The gun should be shaded as well and a slightly different tone of green to make the add-on pop out. Finally, the treads should be painted black to give a feeling of grip and ruggedness.