Mean colours (no correction for interstellar reddening) for C stars derived from the Fourier-mean JHK magnitudes listed in Table 3 of Whitelock et al. (2006) for all Miras (i.e., their variability type 1n) and all non-Miras (i.e., their class 2n). Each point represents the time average of temporal variations (as shown in Fig. 14 for a subsample of the targets included here) for a specific object. The dashed line represents the fit given in Eq. (7) of Whitelock et al. (2006) for the Mira sample prior to de-reddening. In addition, the photometric data collected by Bergeat et al. (2001; Table 4) is overplotted as well as synthetic colours from a sub-grid of the hydrostatic COMARCS models presented in Paper I for comparison.