This study assesses the effects of colour-blindness on casual computer gaming performance and experience. Participants played an online puzzle game in both an unmodified environment and in a colour-blind simulation. Quantitative information collected suggests that the colour-blind filter did not negatively impact player performance. However, post-test questionnaires reveal that users perceived the game to be more difficult and their performance as limited. These contradicting results highlight the importance of further assessing the impact of colour vision deficiency on performance, and the accessibility principles used in game design when colour coding operable cues.