How does a phenol red-containing solution look if co2 level is high?

The variables to be examined in relation to carbon dioxide use are the amount of light exposure and amount of dissolved CO2. Phenol red is yellow/orange under acidic conditions, that is when the pH of the solution is less than 7 (e.g. pH = 6). This occurs when the concentration of CO2 is high.

The mass has escaped into a gas which you can not see so the law stays true.