  Previous studies have shown that for the Supernova Legacy Survey three-year
(SNLS3) data there is strong evidence for the redshift-evolution of
color-luminosity parameter $\beta$ of type Ia supernovae (SN Ia). In this
paper, we explore the effects of varying $\beta$ on the cosmological
constraints of holographic dark energy (HDE) model. In addition to the SNLS3
data, we also use Planck distance prior data of cosmic microwave background
(CMB), as well as galaxy clustering (GC) data extracted from Sloan Digital Sky
Survey (SDSS) data release 7 and Baryon Oscillation Spectroscopic Survey
(BOSS). We find that, for the both cases of using SN data alone and using
SN+CMB+GC data, involving an additional parameter of $\beta$ can reduce
$\chi^2$ by $\sim$ 36; this shows that $\beta$ deviates from a constant at
6$\sigma$ confidence levels. Adopting SN+CMB+GC data, we find that compared to
the constant $\beta$ case, varying $\beta$ yields a larger fractional matter
density $\Omega_{m0}$ and a smaller reduced Hubble constant $h$; moreover,
varying $\beta$ significantly increases the value of HDE model parameter $c$,
leading to $c\approx 0.8$, consistent with the constraint results obtained
before Planck. These results indicate that the evolution of $\beta$ should be
taken into account seriously in the cosmological fits. In addition, we find
that relative to the differences between the constant $\beta$ and varying
$\beta(z)$ cases, the effects of different light-curve fitters on parameter
estimation are very small.
