The neural mechanisms by which information is maintained in working memory are challenging to study, as such maintenance is not always correlated with detectable sustained neural activity. Perturbation of the memory network with a visual impulse has proven useful to probe memoranda in such activity-quiescent states. However, the impulse perturbation approach has so far been applied exclusively to spatially localized or spatially referenced stimuli, such as orientations or tone frequencies. It is unknown whether the neural maintenance mechanisms of non-spatial memoranda would be analogous. In the present study we therefore applied the impulse perturbation method to working memory for colours, which are intrinsically non-spatial stimuli, focusing on a set of pre-registered analyses. We analysed the EEG data of 30 participants who completed a delayed match-to-sample working memory task, in which one of the two items that were presented was retro-cued as task-relevant. We assessed the colour space underlying memory maintenance, and found that both cued and uncued colours were decodable from impulse-evoked activity, the latter in contrast to previous reports of working memory for orientation gratings. We furthermore examined colour decoding from ongoing oscillations in the alpha band, and found that cued items could be decoded therein, whereas uncued items could not, which might be mediated by attention. Overall, the outcomes suggest that subtle differences exist between the representation of colours and that of stimuli with spatial properties, but the present results also demonstrate that regardless of their specific neural state, both are accessible through visual impulse perturbation.