  Optical and near-IR observations of the halos of disk galaxies and blue
compact galaxies have revealed a very red spectral energy distribution, which
cannot easily be reconciled with a normal, metal-poor stellar population like
that in the stellar halo of the Milky Way. Here, spectral evolutionary models
are used to explore the consequences of these observations. We demonstrate that
a stellar population of low to intermediate metallicity, but with an extremely
bottom-heavy initial mass function, can explain the red halos around both types
of objects. Other previously suggested explanations, like nebular emission or
very metal-rich stars, are shown to fail in this respect. This indicates that,
if the reported halo colours are correct, halo populations dominated by
low-mass stars may be a phenomenon common to galaxies of very different Hubble
types. Potential tests of this hypothesis are discussed, along with its
implications for the baryonic dark matter content of galaxies.
