  Using Darboux transformation one can construct infinite family of potentials
which lead to the flat spectrum of scalar field fluctuations with arbitrary
multiple precision, and, at the same time, with "essentially blue" spectrum of
perturbations of metric. Besides, we describe reconstruction problem: find
classical potential V(phi) starting from the known "one-loop potential" u(t) =
d^2V(phi(t))/d phi(t)^2.
