Final answer:
The immediate source of colored light in neon signs is the gas that fills the sign tube.
Step-by-step explanation:
Neon signs emit colored light due to the gas discharge process. The immediate source of colored light in neon signs is the gas that fills the sign tube.
The red-orange color, which is the most commonly associated with neon signs, is actually emitted by the gas neon itself. Other colors in neon signs are produced by using different gases or mixtures of gases. For example, blue light can be produced using mercury discharges and yellow light can be produced using sodium discharges.
When an electrical current passes through the gas at low pressure, the gas atoms are excited to a higher energy state. As the atoms decay back to the ground state, they emit light, creating the colored glow of neon signs.