Why are some objects seen as colorless?

In atoms and molecules the electrons surround the nucleus in energy levels. When an electron is not exited it usually occupies the lowest energy level available. When energy is given to an electron it moves up a different amount of energy levels depending on how much energy it gains. The distance between the energy levels decreases further away from the nucleus until the electron completely has escaped the nucleuses attraction. When this occurs, the atom or molecule has been ionized.   

When photons of light hit atoms or molecules, the electrons absorb this energy. In order for electrons to move to the next energy level the light need to be of a minimum frequency. This is as the electrons cannot rest in between energy levels. The amount of energy needed for electrons to move to the next energy levels is called a “quanta”. When electrons fall back to their ground state the same amount of energy is released in form of photons. It takes different frequencies to raise electrons of different atoms and molecules to different energy levels. This is what gives different colors.  

The visible light we see is only a small part of a much larger electromagnetic spectrum. The human eye only interprets a narrow range of frequencies. Photons that travel either below or above these frequencies are seen as colorless. Examples of theses are ultraviolet rays, x-rays and radio waves. Some materials have electrons that require a quantum of energy that is outside the frequencies of visible light. This means that they do not give off any photons and make perfect translucent glass.