How to interpret psychology from heart rate variability?

In this paper, we have used the color stimuli to define the arousal level of subjects by analyzing their heart rate variability (HRV). For this analysis, we have used the novel Triangular Phase Space Mapping (TPSM) and try to distinguish two groups of emotions, calm and energetic. The results show that cold colors are associated with low arousal level and hot colors are in relation with high arousal level.