Decision making acts as the basis of our behaviors. This study aims to experimentally clarify how environments influence the risk evaluation stages in humans' decision-making processes. Because color is an environmental attribute which can affect human temperament, we conducted a psychological experiment to investigate if environmental colors can influence humans' risk evaluation. Given that the Iowa Gambling Task (IGT) is a widely-used measure of risk-taking propensity, we analyzed the subjects' IGT net scores and the subjects' choice behaviors that they took after their big losses. These behaviors were considered ordinary in both daily-life environments and specially colored environments. The results showed that the subjects in the blue room tended to be conservative. Conversely, the subjects in the red room tended to take risks. It suggests that red environments may inhibit positive affect.