I would suggest beginning by coloring the two figures that are standing close together with a light grey or silver. Use white to add highlights to the suits they are wearing and to brighten up the coloring of the helmets. Their visors could be colored a light green, while the liquids running down each of their arms should be colored green and red.
For the third figure, lying on the ground, begin by adding a darker grey or black to their suit. As for the liquid around them, use a dark green to get the desired effect. Make their eyes white with a light blue in the center to make them pop. Outline each figure and the liquid with a darker color for definition. To finish things off, use black to add some shadows in the appropriate spots.