In an experiment, a colour change is observed, and also observed is prolonged bubbling. Is this a chemical change?
Chemical change is characterized by the formation of new substances, and the making and breaking of strong chemical bonds. This is usually signalled by a color change, because the evolution of gases is not always apparent.
Your example clearly represents a chemical change, as you have (i) observed a colour change, (ii) observed the formation of a new substance, the gas.