  FS Aur is famous for a variety of uncommon and puzzling periodic photometric
and spectroscopic variabilities. It was previously proposed that the precession
of a fast-rotating magnetically accreting white dwarf can successfully explain
these phenomena. We present a study of FS Aur based on two extensive sets of
optical photometric observations and three X-ray data sets in which we intended
to verify whether the observational properties of the long period modulations
observed in FS Aur and V455 And are similar in appearance to the spin
modulation in ordinary IPs. These new optical observations have revealed, for
the first time in photometric data, the variability with the presumed
precession period of the white dwarf, previously seen only spectroscopically.
We also found that the modulations with the precession and orbital periods are
evident in X-ray data. We show that the observed properties of FS Aur closely
resemble those of other intermediate polars, thus confirming this cataclysmic
variable as a member of the class.
  Our analysis of multicolour observations of intermediate polars has shown
that time-series analysis of colour indices appears to be a powerful technique
for revealing hidden variabilities and shedding light on their nature. We have
found that the (B-I) power spectrum of V1223 Sgr indicates the presence in the
data of the spin pulsation which is not seen in the optical light curve at all.
Also, the analysis of the colour indices of V455 And revealed the presence of
the photometric variations which, similarly to FS Aur, was previously observed
only spectroscopically.
