Distributions of the mass fraction X of the passive scalar in simulations of the Kelvin–Helmholtz instability with the initial Mach number $\mathcal{M}$₀ = 10⁻² on a 128 × 64 grid. The results are shown at t = 0.8 $\mathcal{M}$₀⁻¹. Rows and columns show different reconstruction schemes and numerical flux functions, respectively. The color scale intentionally shows values X < 0 and X > 1 to highlight the overshoots that some of the schemes produce. The absolute value of the largest overshoot outside of this range is given in each panel.