  A review of the spatially flat cosmological model SU(2)$_{\rm CMB}$,
minimally induced by the postulate that the Cosmic Microwave Background (CMB)
is subject to an SU(2) rather than a U(1) gauge principle, is given.
Cosmological parameter values, which are determined from the Planck CMB power
spectra at small angular scales, are compared to their values in spatially flat
$\Lambda$CDM from both local and global extractions. As a global model
SU(2)$_{\rm CMB}$ leans towards local $\Lambda$CDM cosmology and is in tension
with some global $\Lambda$CDM parameter values. We present spectral
antiscreening / screening effects in SU(2)$_{\rm CMB}$ radiance within the
Rayleigh-Jeans regime in dependence on temperature and frequency. Such radiance
anomalies can cause CMB large-angle anomalies. Therefore, it is pointed out how
SU(2)$_{\rm CMB}$ modifies the Boltzmann equation for the perturbations of the
photon phase space distribution at low redshift and why this requires to the
solve the $\ell$-hierarchy on a comoving momentum grid ($q$-grid) for all $z$.
