Constraints on the a − λ plane, resulting from M_max > 2  M_⊙, obtained assuming SR EOS of baryon matter, and for purely CFL cores (no 2SC layer) starting at ρ_CFL = 1.7ρ₀,...,4.0ρ₀. Densities 2.3ρ₀ and 3.0ρ₀ correspond to P₁ and P₂, relevant for the boundaries of the 2SC layer in a 2SC+CFL core. Each line is an upper boundary of the region of (a_CFL,λ_CFL) consistent with M_max > 2  M_⊙. These lines are labeled by the density at which a direct transition B→Q(CFL) takes place.