Here's why:

* Physical changes alter the form or appearance of a substance but not its chemical composition. Examples include melting ice (solid to liquid), cutting paper, or dissolving sugar in water.

* Chemical changes result in the formation of new substances with different chemical compositions. Examples include burning wood, rusting metal, or cooking an egg.

Color is a physical property, meaning it can be observed without changing the substance's chemical makeup. So, something becoming colorless (or changing color) is a physical change, as long as the chemical composition of the substance itself remains the same.

However, a change in color can sometimes be a sign of a chemical reaction. For example, if a piece of metal rusts (turns reddish-brown), this is a chemical change because the metal has reacted with oxygen to form a new substance (iron oxide).