  We make use of individual (epoch) detection data from the Pan-STARRS 3Pi
survey for 2863 optical ICRF3 counterparts in the five wavelength bands g, r,
i, z, and y, published as part of the Data Release 2. A dedicated method based
on the Functional Principal Component Analysis is developed for these sparse
and irregularly sampled data. With certain regularization and normalization
constraints, it allows us to obtain uniform and compatible estimates of the
variability amplitudes and average magnitudes between the passbands and
objects. We find that the starting assumption of affinity of the light curves
for a given object at different wavelengths is violated for several percent of
the sample. The distributions of root-mean-square variability amplitudes are
strongly skewed toward small values, peaking at ~0.1 mag with tails stretching
to 2 mag. Statistically, the lowest variability is found for the r band and the
largest for the reddest y band. A small "brighter-redder" effect is present,
with amplitudes in y greater than amplitudes in g in 57% of the sample. The
variability versus redshift dependence shows a strong decline with z toward
redshift 3, which we interpret as the time dilation of the dominant time
frequencies. The colors of radio-loud ICRF3 quasars are correlated with
redshift in a complicated, wavy pattern governed by the emergence of brightest
emission lines within the five passbands.
