We discuss two aspects of the color dipole picture of high energy
photon-proton scattering. First we present bounds on various ratios of deep
inelastic structure functions resulting from the dipole picture that, together
with the measured data, can be used to restrict the kinematical range of its
applicability. The second issue that we address is the choice of energy
variable in the dipole-proton cross section.Comment: 6 pages; talk presented by C.E. at 12th International Conference on
Elastic and Diffractive Scattering (EDS07), DESY Hamburg, May 200
