Mutations in the genes influencing melanocytes not only affect the colour of an animal, but are also believed to impact physiological and behavioural functions. When this is taken into consideration, the common perception among horse owners that the chestnut coat colour is associated with adverse behaviours seems plausible. The aim of this study was to explore this perception by providing insight into any potential genetic associations between coat colour and adverse behaviours in horses. Data were acquired through an internationally accessible online questionnaire. Respondents provided information on their horse’s behaviour during general handling, whilst being exercised, towards different stimuli in their environment and when isolated from other horses. Analyses considered behavioural data on 477 horses that represented a range of breeds, ages, and event disciplines. The breed, sex, and age of the horse significantly (P < 0.05) influenced many of the equine behaviours assessed in the questionnaire. Significant differences in behavioural responses between bay and chestnut horses were only present for four questions. No evidence was found to support that chestnut horses are more likely than bay horses to display behaviours often associated with training difficulties. However, chestnut horses were more likely to approach objects and animals in their environment, regardless of their familiarity. This suggests that selection for the chestnut phenotype in horses may have inadvertently involved selection for boldness and altered the way horses interact with their surroundings.