Here we show the stellar population that is the input to the simulated images (upper panels) and the output photometry measured (lower panels), in (K,J − K) and (K,I − K), assuming a surface brightness, μ_V = 19 mag/arcsec², for the stellar population defined in Fig. 4. The two distinct star formation episodes are colour coded, so that the impact of the different filter choices can be better judged.