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Source of light
When meteoroids enter the Earth's atmosphere, they collide with numerous air molecules. Those collisions sputter away the outer layers of the particle, creating a vapor of sodium, iron and magnesium atoms. In subsequent collisions, electrons are knocked into orbits at larger mean distances from the nucleus of the atoms. When the electrons fall back to their rest positions, light is emitted. This is the same process as in gas discharge lamps.

Colors of meteors
The color of many Leonids is caused by light emitted from metal atoms from the meteoroid (blue, green, and yellow) and light emitted by atoms and molecules of the air (red). The metal atoms emit light much like in our sodium discharge lamps: sodium (Na) atoms give an orange-yellow light, iron (Fe) atoms a yellow light, magnesium (Mg) a blue-green light, ionized calcium (Ca+) atoms may add a violet hue, while molecules of atmospheric nitrogen (N2) and oxygen atoms (O) give a red light. The meteor color depends on whether the metal atom emissions or the air plasma emissions dominate.