  Driven by the CMB temperature-redshift ($T$-$z$) relation as demanded by
deconfining SU(2) Yang-Mills thermodynamics, an according cosmological model is
proposed and analysed. This model -- SU(2)$_\CMB$ -- exhibits a dark sector,
representing $\Lambda$CDM with a certain late-time dark-matter density which
transitions to a reduced (present-day) density parameter at high $z$. We
statistically analyse constraints on cosmological parameters directly imposed
by the values of the standard co-moving ruler $r_d$ and the angular size of the
sound horizon $\theta_*$. Compared to the $\Lambda$CDM best fit to 2015 Planck
data, we require an increased (present-day) dark matter density when $r_d\cdot
H_0=$\,const and a value $H_0\sim 73.5$ km\,s$^{-1}$Mpc$^{-1}$ -- typical for
local extractions -- are used. The ratio between the density parameters of
primordial and late-time dark matter ranges between 0.5 and 0.7. We confirm
this trend by fitting the predictions of SU(2)$_\CMB$, obtained from a modified
CLASS code, to the angular power spectra TT, TE, and EE. We consider adiabatic,
scalar primordial curvature perturbations and distinguish two treatments of
thermal quasi-particles in the perturbation equations. Best fits predict a
red-tilted primordial power spectrum. Moreover, a low baryon density is
obtained compared with the coincidence value of BBN, the $\Lambda$CDM best fit
of the 2015 Planck data, and the observed deuterium abundance. Our derived
values of $H_0$ support the results of local cosmological observations. Also,
there is a tendency for late reionisation.
