Here are the synonyms that best fit each sentence based on the context provided:
1. The painting is a wonderful **melody** of light and dark.
2. The two countries signed a treaty so they could live in **peace**.
3. The two candidates’ opinions were in **agreement** on that issue.
You can check trusted online dictionaries like Merriam-Webster, Oxford English Dictionary, or Dictionary.com for the definitions of the chosen synonyms to ensure they fit the context correctly.