Final answer:
Fireplace crystals change the flame's color by introducing certain metal ions into the combustion process. Evidence from color observations supports this explanation.
Step-by-step explanation:
Fireplace crystals change the flame's color by introducing certain metal ions into the combustion process. These metal ions emit different wavelengths of light when they return to their ground states, resulting in varied flame colors. For example, copper ions produce a green flame, while strontium ions produce a red flame.
Evidence from color observations supports this explanation. By conducting flame tests, which involve introducing different metal ions into a flame, scientists have observed the correlation between specific metal ions and flame colors. This experimental evidence confirms the connection between fireplace crystals and the change in flame color.