The colour white results from combining many different wavelengths at equal intensities. Here, Weiss et al. asked participants to rate the perceptual similarity of various odorant mixtures to see if an 'olfactory white' could be generated. The presented mixtures were increasingly complex, featuring rising numbers of equally intense odorants that together increasingly filled the stimulus space. The participants found that mixtures of ∼30 odorants started to smell alike, even if they contained no common components, suggesting that an olfactory white can be generated and that it relies on the characteristics of sets of molecules rather than the identities of individual molecules.