  Recent, high precision photometry of Omega Centauri, the biggest Galactic
globular cluster, has been obtained with Hubble Space Telescope. The color
magnitude diagram reveals an unexpected bifurcation of colors in the main
sequence (MS). The newly found double MS, the multiple turnoffs and subgiant
branches, and other sequences discovered in the past along the red giant branch
of this cluster add up to a fascinating but frustrating puzzle. Among the
possible explanations for the blue main sequence an anomalous overabundance of
helium is suggested. The hypothesis will be tested with a set of FLAMES@VLT
data we have recently obtained (ESO DDT program), and with forthcoming ACS@HST
images.
