  The relationship between the coincidence indices of a lattice $\Gamma_1$ and
a sublattice $\Gamma_2$ of $\Gamma_1$ is examined via the colouring of
$\Gamma_1$ that is obtained by assigning a unique colour to each coset of
$\Gamma_2$. In addition, the idea of colour symmetry, originally defined for
symmetries of lattices, is extended to coincidence isometries of lattices. An
example involving the Ammann-Beenker tiling is provided to illustrate the
results in the quasicrystal setting.
