Аннотация:On the basis of photoelectric UBV observations of irregular variable stars it has been shown that the dependence between the V-brightness and colour indices (B-V) and (U-B) is not a monotonous one. At the diminution of the star brightness from the maximum to some medium value colour, indices increase at average but at the further brightness diminution they decrease (the star becomes bluer at the minimum of its brightness). Such a heterogeneous dependence is inherent not only to the irregular variables of early and late classes but also to the T Tauri stars.