  A multicomponent mixture of Janus colloids with distinct catalytic coats and
phoretic mobilities is a promising theoretical system to explore the collective
behavior arising from nonreciprocal interactions. An active colloid produces
(or consumes) chemicals, self-propels, drifts along chemical gradients, and
rotates its intrinsic polarity to align with a gradient. As a result the
connection from microscopics to continuum theories through coarse-graining
couples densities and polarization fields in unique ways. Focusing on a binary
mixture, we show that these couplings render the unpatterned reference state
unstable to small perturbations through a variety of instabilities including
oscillatory ones which arise on crossing an exceptional point or through a Hopf
bifurcation. For fast relaxation of the polar fields, they can be eliminated in
favor of the density fields to obtain a microscopic realization of the
Nonreciprocal Cahn-Hilliard model for two conserved species with two distinct
sources of non-reciprocity, one in the interaction coefficient and the other in
the interfacial tension. Our work establishes Janus colloids as a versatile
model for a bottom-up approach to both scalar and polar active mixtures.
