Some color–color plots containing our sample of observed carbon stars (black symbols) and the models (colored diamonds). The triangles are for stars from Group A, the circles for Group B, the stars for Group C, and the squares for Group D. The open diamonds represent the models at solar (in blue) and subsolar metalliticity (red). The bars show the ± 1σ root-mean-square deviation of our photometry with respect to the literature (large-amplitude variables excluded). This is an upper limit of the uncertainties in the flux calibration and any possible residual variability.