Near-infrared (J-H vs H-Ks) colour-colour diagram of the P4 sample targets. The grey circles highlight the outliers in this diagram. The solid red line shows the mean colours of dwarfs from Pecaut & Mamajek (2013). The cyan line indicates the subset of stars from M0V to M6V. The inset provides a zoomed-in view of the high-density core of the distribution, allowing better visualisation of the main-sequence locus. The typical errors in the colours are indicated in the bottom right corner.