  Results of neutrino oscillation experiments have always been presented on the
(sin^2 2theta, Delta m^2) parameter space for the case of two-flavor
oscillations. We point out, however, that this parameterization misses the half
of the parameter space pi/4 < theta <= pi/2 (``the dark side''), which is
physically inequivalent to the region 0 <= theta <= pi/4 (``the light side'')
in the presence of matter effects. The MSW solutions to the solar neutrino
problem can extend to the dark side, especially if we take the conservative
attitude to allow higher confidence levels, ignore some of the experimental
results in the fits, or relax theoretical predictions. Furthermore even the
so-called ``vacuum oscillation'' solution distinguishes the dark and the light
sides. We urge experimental collaborations to present their results on the
entire parameter space.
