Final answer:
Electron transitions within atoms emit or absorb photons, which may be visible as colored light depending on their wavelength, although atoms and subatomic particles themselves do not possess color in the conventional sense.
Step-by-step explanation:
When an electron jumps between energy levels within an atom, it emits or absorbs a photon, which can manifest as visible light.
The color perceived is determined by the wavelength of the emitted photon. For example, a photon with a wavelength of 380 nm appears blue, while one with 720 nm appears red. Atoms as a whole do not have a color because color is a property of light, not of matter. However, the aggregate of photons emitted or absorbed by a substance can give it a characteristic color.
As for subatomic particles, they themselves do not have color in the sense that we experience with light. Instead, 'color' in particle physics refers to a form of charge related to the strong force and has nothing to do with the colors in the visible spectrum.