  We present the results of our analysis of the photometric data of globular
clusters in the elliptical galaxy NGC 5128 (Cen A). We show that the integrated
colour U-B can be an effective metallicity indicator for simple stellar
populations. This is because it is sensitive to metallicity via the opacity
effect but relatively insensitive to the effective main sequence turn-off
temperature of the population (and thus to age) when Teff ~ 7000-12000K, that
is, when the Balmer Jump is strong. This flat U-B vs Teff relation is a result
of the fact that the blueing effect of the optical continuum with increasing
temperature is temporarily stopped by the Balmer Jump which becomes greater
with temperature in this range. In this study we use U-B and B-V as metallicity
and age indicators, respectively. We first show that the use of the U-B vs B-V
two-colour diagram roughly yields the metallicities and ages of the Milky Way
globular clusters independently determined, and then apply the technique to the
clusters in NGC 5128. There is a large range in U-B, which corresponds to
[Fe/H] of -2.0 through over +0.3. The large uncertainties from the data and the
models currently prevent us from pinning down their ages and metallicities.
Although a constant age for all these clusters cannot be ruled out, there is a
hint of the metal-rich clusters being younger. Significance of these results
and caveats of the analysis are discussed.
