  The spectrum of temporal fluctuations of total magnetic energy for several
dynamo models is different from white noise at frequencies smaller than the
inverse of the turnover time of the underlying turbulent velocity field.
Examples for this phenomenon are known from previous work and we add in this
paper simulations of the G.O. Roberts dynamo and of convectively driven dynamos
in rotating spherical shells. The appearance of colored noise in the magnetic
energy is explained by simple phenomenological models. The Kolmogorov theory of
turbulence is used to predict the spectrum of kinetic and magnetic energy
fluctuations in the inertial range.
