  A quantum collision model (CM), also known as repeated interactions model,
can be built from the standard microscopic framework where a system S is
coupled to a white-noise bosonic bath under the rotating wave approximation,
which typically results in Markovian dynamics. Here, we discuss how to
generalize the CM construction to the case of frequency-dependent system-bath
coupling, which defines a class of colored-noise baths. This leads to an
intrinsically non-Markovian CM, where each ancilla (bath subunit) collides
repeatedly with S at different steps. We discuss the illustrative example of an
atom in front a mirror in the regime of non-negligible retardation times.
