Amplitudes of the K-band photometric variations of the C-type Miras listed in Table 3 of Whitelock et al. (2006) plotted against the corresponding mean colour indices which are corrected for interstellar reddening and given in Table 6 of Whitelock et al. (2006). The dotted line was fitted to guide the eye. Overplotted are the values resulting from the different atmospheric models. Note, that model S exactly reproduces the data of RU Vir which is, therefore, plotted with a different symbol than in other figures.