In traditional neon tubes, different colors are created by filling the tubes with various gases and coating the inside surface of the tube with different phosphors or fluorescent powders. When an electrical current passes through the gas in the tube, it excites the gas atoms, causing them to emit photons of light. The color of the emitted light depends on the type of gas used and the specific characteristics of the phosphor coating.

Here are some common gases and their associated colors in traditional neon tubes:

1. Neon (red-orange): The most common gas used in traditional neon signs, it emits a red-orange glow when excited.
2. Argon (blue): Argon gas emits a blue glow when ionized. Sometimes argon is mixed with mercury to produce a bluish light.
3. Helium (pink): Helium gas emits a pinkish glow when ionized, but it's not commonly used in neon signs due to its scarcity and higher cost.
4. Krypton (green): Krypton gas emits a greenish glow when ionized, and it's occasionally used in neon signs to achieve green hues.

The color of the light emitted by the gas can be further modified by using different phosphors or fluorescent coatings inside the tube. These coatings interact with the light emitted by the gas, producing additional colors or enhancing certain color tones. For example, adding a phosphor that emits blue light can modify the color of the neon gas to produce a purple glow.

In LED neon lights, colors are typically produced by using different combinations of colored LEDs rather than gases and phosphors. LED neon lights offer a wider range of colors and are more energy-efficient compared to traditional neon tubes.