Colour–colour diagram of sources selected from two grid regions in Fig. 5. Sources in black are assumed to be representative of genuine NGC 6822 and MW foreground, whilst sources in red are assumed to be representative of MW sources only, as described in the text. The horizontal line at (J − H)₀ = 0.72 mag has been used to separate the galaxy and the foreground stellar population. The upper diagonal line at (J − K)₀ = 1.20 mag represents the colour boundary between C- and M-type AGB stars applied to the sample (see Sect. 3.3). The second diagonal line at (J − K)₀ = 0.80 mag relates to an alternative foreground removal method discussed in Sect. 5.4.3.