The present study explored the effects of colour upon challenge and threat states, using 24 a within-subjects design. Eighteen academic students and staff indicated how they 25 perceived a novel task competition when instructions were presented in one of four 26 colours. For each session participants were required to fill in one questionnaire 27 measuring self-reported challenge and threat states, and be connected to a Finometer 28 measuring psychophysiological changes to cardiac output and total peripheral 29 resistance during the competition. The results suggest that the perception of challenge 30 was only influenced by the colour green, which was significantly higher than red, 31 black, and blue. The perception of threat was not significantly influenced by any 32 colour, nor were there any significant differences in psychophysiological measures 33 across colours. Furthermore, no colour significantly influenced performance when 34 compared. The findings advise the use of green in aiding the perception of challenge 35 within a competitive situation. However, due to the findings of this study opposing 36 much of the previous literature, caution should be taken in applied settings.