J − W2 versus Y − J colour–colour plots for the UKIDSS T dwarfs with YJ and WISE photometry and benchmark systems from the literature, along with new photometry and benchmarks presented in this paper. Benchmark systems with roughly solar metallicity are shown in green, whilst those with subsolar metallicity are shown in blue. Model colour tracks for Saumon et al. (2012), top panel, and Morley et al. (2012), bottom panel, are shown for comparison. The latter assumed f_sed = 5. The models shown are all solar metallicity, and the T_eff and log g values are indicated on the colour sequences. Each benchmark object is linked to a 1σ box indicating the model prediction for its colours.