  The globular cluster omega Centauri contains the largest known population of
very hot horizontal branch (HB) stars. We have used the Hubble Space Telescope
to obtain a far-UV/optical color-magnitude diagram of three fields in omega
Cen. We find that over 30% of the HB objects are ``extreme'' HB or hot post-HB
stars. The hot HB stars are not concentrated toward the cluster center, which
argues against a dynamical origin for them. A wide gap in the color
distribution of the hot HB stars appears to correspond to gaps found earlier in
several other clusters. This suggests a common mechanism, probably related to
giant branch mass loss. The diagram contains a significant population of hot
sub-HB stars, which we interpret as the ``blue-hook'' objects predicted by
D'Cruz et al. (1996a). These are produced by late He-flashes in stars which
have undergone unusually large giant branch mass loss. omega Cen has a
well-known spread of metal abundance, and our observations are consistent with
a giant branch mass loss efficiency which increases with metallicity.
