It is known that the number of colours necessary to colour each point of 3-space so that no two points lying distance 1 apart have the same colour lies between 5 and 18. All optimal colourings (which establish the upper bound for ) have to date been found using lattice–sublattice colouring schemes. This paper shows that in such colouring schemes must use at least colours to have an excluded distance. In addition this paper constructs a 1-excluded colouring of using a lattice–sublattice scheme with 15 colours—the least number of colours possible for such schemes.