  Recently, there has been growing interest on primordial ``blue" ($n>1$)
perturbation spectra, motivated both by a composite set of observational data
on large scales and from the point of view of theoretical model building. After
reviewing the theoretical (inflationary) motivations for these blue spectra, we
consider various observational constraints, within both Cold Dark Matter and
Mixed Dark Matter scenarios. In particular, using linear theory, we discuss
large--scale bulk flows and the X--ray cluster abundance. We also perform
various N--body simulations of these models to study the clustering properties
of the matter distribution and the peculiar velocity field.
