Study how brine shrimp are attracted to blue light, but not red light. Discuss how this adaptation might help them survive: they will be able to see the blue light that penetrates greater water depths, and use it to find their way to the surface. The food they eat, green algae, lives at the surface.
(Optional: show how pond organisms (e.g. cyclops) are attracted to light, to show that light attraction is a general phenomenon.)

Use filters to visualize an ocean scene, where only blue light has penetrated. Observe that animals that are coloured red or dark are less visible than lighter-coloured animals, and understand how their colouring would camouflage them from predators.