* Chemical changes involve the formation of new substances with different properties, including color.

* For example, rusting iron (a chemical change) turns the metal from silvery to reddish-brown.

* Burning wood (a chemical change) turns the wood black and produces ash.

* Physical changes alter the form or appearance of a substance but don't change its chemical composition.

* Melting ice (a physical change) changes the state of water from solid to liquid but doesn't change its chemical makeup (H₂O).

* Dissolving sugar in water (a physical change) disperses the sugar molecules but doesn't change their chemical structure.

However, it's not always a guarantee. Some physical changes can also cause color changes. For example:

* Light scattering: A change in the size or shape of particles can cause them to scatter light differently, leading to a color change.

* Pigment mixing: Mixing different colored pigments can create a new color, but this is a physical change, not a chemical reaction.

To be sure about whether a color change indicates a chemical or physical change, you need to consider other evidence. For example:

* Temperature change: Chemical reactions often release or absorb heat.

* Gas production: Many chemical reactions produce gas bubbles.

* Precipitate formation: Chemical reactions can form a solid precipitate that wasn't present before.

In general, if a color change is accompanied by other changes like these, it's a strong indication of a chemical change.