Colour–magnitude diagram containing individual observations of RU Vir adopted from Table 2 of Whitelock et al. (2006) and shifted to an absolute scale M_K by applying the distance modulus derived by the same authors (cf. their Table 6). The dashed line marks the average variation of RU Vir during the light cycle as derived from the Fourier fits in Fig. 8 of Paper II. Overplotted are the corresponding synthetic photometric data of model S. Three different pulsation cycles are plotted with the same symbols, colour-coding, and labels as in Fig. 13 of Paper II. The arrows mark the directions of how the objects pass through the loops during a light cycle, selected phases are labelled (convention for φ_bol / φ_v as in Paper II).