Mean-field models of the nucleon (N) and the delta (Δ) are established with the two-quark vector Richardson potential along with various prescriptions for a running quark mass (single particle) in the Dirac–Hartree–Fock formalism. The N–Δ splitting is obtained from colour magnetic interaction and the results for gA and the magnetic moment are discussed. An effective density dependent one-body potential U(ρ) for quarks at a given density ρ inside the nucleon is derived. Asymptotic freedom and confinement properties are built-in in U(ρ) and the model dependence is restricted to the intermediate densities.