  We propose an alternative model for the holographic dark energy in a non-flat
universe. This new model differs from the previous one in that the IR length
cutoff $L$ is taken to be exactly the event horizon size in a non-flat
universe, which is more natural and theoretically/conceptually concordant with
the model of holographic dark energy in a flat universe. We constrain the model
using the recent observational data including the type Ia supernova data from
SNLS3, the baryon acoustic oscillation data from 6dF, SDSS-DR7, BOSS-DR11, and
WiggleZ, the cosmic microwave background data from Planck, and the Hubble
constant measurement from HST. In particular, since some previous studies have
shown that the color-luminosity parameter $\beta$ of supernovae is likely to
vary during the cosmic evolution, we also consider such a case that $\beta$ in
SNLS3 is time-varying in our data fitting. Compared to the constant $\beta$
case, the time-varying $\beta$ case reduces the value of $\chi^2$ by about 35
and results in that $\beta$ deviates from a constant at about 5$\sigma$ level,
well consistent with the previous studies. For the parameter $c$ of the
holographic dark energy, the constant $\beta$ fit gives $c=0.65\pm 0.05$ and
the time-varying $\beta$ fit yields $c=0.72\pm 0.06$. In addition, an open
universe is favored (at about 2$\sigma$) for the model by the current data.
