What do you need to add in a composition to give 3D objects colors and shadows?

To give 3D objects colors and shadows in a composition, adding light is essential. In a 3D environment within Adobe After Effects, lights simulate the way traditional lights function in the real world, making them crucial for creating realistic shading and highlights on 3D layers.

When you place lights in a composition, they interact dynamically with the 3D objects based on their positioning, intensity, and type (such as point, spot, or ambient lights). This allows for various effects, such as casting shadows on surfaces, creating highlights, and enhancing the overall visual depth of the 3D elements. Without lights, 3D objects would appear flat and lack the depth that shadows and highlights provide.

Other options like a camera serve to view and navigate through the 3D space, while solid and adjustment layers are primarily used for effects and color manipulation but do not inherently create shadows or change the object's appearance in the same way that lighting does. Therefore, the correct approach to add realism and dimension to 3D objects in a composition is by incorporating lights.