Constraints in the (Δ, w₀) plane for models with a late-time phase transition in the dark energy equation of state. The top, middle and bottom panels correspond, respectively, to Models B, C, and L described in the text. In all cases the Hubble constant has been kept fixed at H₀ = 70 km s⁻¹ Mpc⁻¹, the black contours denote the one, two and three-sigma confidence levels, and the colourmap depicts the reduced chi-square of the fit for each set of model parameters (a dark red colour corresponds to a reduced chi-square of three or larger).