The spheres representing nitrogen and oxygen are different colors because the two elements have different atomic structures. Nitrogen has seven electrons, six of which are in the outer shell, while oxygen has eight electrons, seven of which are in the outer shell. This difference in electron configuration gives the two elements different chemical properties, including different colors.

In general, the color of an object is determined by the way it interacts with light. When light hits an object, some of the light is absorbed and some is reflected. The color of the object is determined by the wavelengths of light that are reflected.

In the case of nitrogen and oxygen, the difference in electron configuration causes the two elements to absorb and reflect different wavelengths of light. Nitrogen gas is colorless, while oxygen gas is pale blue. This is because nitrogen gas absorbs light in the red and violet regions of the spectrum, while oxygen gas absorbs light in the red and yellow regions of the spectrum.

The different colors of nitrogen and oxygen are also reflected in their physical properties. Nitrogen gas is a colorless, odorless, and tasteless gas that is lighter than air. Oxygen gas is a colorless, odorless, and tasteless gas that is slightly heavier than air.