All e-liquid should be stored at room temperature, ~21°C (70°F). This will ensure that it keeps its flavor, strength (if nicotine is present), and freshness.
Depending on the conditions (specifically heat, light and air), e-liquid may change in color due to oxidation or the nicotine in the liquid. It certainly doesn’t make it go bad, but it may change the taste, and if left for a long time, may make the taste and strength get weaker over time. The process happens slowly over time, and is much slower if stored in sealed and dark conditions. Presence of oxygen, heat and light accelerate the process.