Each brush corresponds to a key correcting concealer colour to avoid colour mixing.
Darkness correcting brush: cover + conceal darkness with peach - push + blend a peach shaded corrector over dark spots and dark circles.
Dullness correcting brush: brighten with pink - push + blend a pink shaded corrector over dark areas.
Sallowness correcting brush: cancel sallowness with lavender - push + blend a lavender shaded corrector over sallow areas.
Redness correcting brush: neutralise redness with green - push + blend a green shaded corrector over areas that look red.