Carbon dioxide (CO2) is colorless. In its gaseous state, it's invisible in the air. Liquid CO2 is also colorless, similar to water. Even solid CO2, known as dry ice, appears white, much like frost. This is due to the scattering of light on its surface, not an inherent color.
Different States of CO2 and Their Appearance
- Gaseous CO2: Invisible and colorless.
- Liquid CO2: Colorless, like water.
- Solid CO2 (Dry Ice): White, due to light scattering on the frosty surface.
It's important to note that the color you observe in some contexts involving CO2 isn't the color of the CO2 itself but rather a result of other factors. For example:
- CO2 indicators: These devices change color to indicate CO2 levels, but the color change is due to a chemical reaction within the indicator, not the CO2's inherent color. Examples include the color change in planted tank CO2 indicators (from pink to white, or other variations) as shown in several of the provided links.
- CO2 lasers: These lasers utilize CO2 gas but the "color" of the laser is infrared and invisible to the human eye; the effects of the laser on certain materials might appear as color changes on those materials.
- CO2 gas discharge tubes: When energized, CO2 gas glows. The color depends on the gas pressure and the energy applied but is not inherently the color of CO2 at rest.
The color of a CO2 atmosphere, as discussed in one of the links, would appear similar to Earth's sky, mainly due to Rayleigh scattering which preferentially scatters shorter wavelengths of light (blue). This is because of the interaction of light with the atmospheric particles and not the inherent color of the CO2. The CO2 itself remains colorless. The references provided also corroborate the colorless nature of CO2 in its various forms.
