  The reionization of the intergalactic medium at redshifts $z\gtrsim 6$ is
expected to have a lasting impact on galaxies residing in low-mass dark matter
halos. Unable to accrete or retain gas photo-heated to temperatures $T \gtrsim
10^4$ K, the star formation histories of faint galaxies in the early Universe
are expected to decline as they exhaust their gas supply, resulting in a
turn-over in the galaxy luminosity function (LF) and a potential solution to
the missing satellites problem in the local group. Unfortunately, there are
several challenges to constraining `reionization feedback' empirically, most
notably that galaxies in low-mass halos are intrinsically faint, and that there
are other physical mechanisms capable of inducing a turn-over in the LF. In
this work, we investigate a new signature of reionization feedback that is in
principle distinct from other processes: as faint galaxies are quenched by
reionization, their stellar populations passively age and grow redder while the
brighter galaxies nearby continue to form stars at an increasing rate and so
remain relatively blue. We find that this contrast, between quenched and
un-quenched galaxies induces a scale and colour-dependent signature in the
present-day near-infrared background comparable to the expected sensitivity of
NASA's upcoming SPHEREx mission. Whereas models with pure mass suppression
largely affect the signal at wavelengths $\lesssim 2 \mu\rm{m}$, $\sim
5$%-level differences in the background persist out to $\sim 5 \mu\rm{m}$ for
reionization feedback models. Finally, the power spectra of intensity ratio
maps exhibit larger variations, and may thus be a promising target for future
analyses.
