  We present a theoretical calibration of the RR Lyrae period-luminosity-color
and period-color-color relations in the multiband uvby Stroemgren photometric
system. Our theoretical work is based on calculations of synthetic horizontal
branches (HBs) for four different metallicities, fully taking into account
evolutionary effects for a wide range in metallicities and HB morphologies.
While our results show that "pure" period-luminosity and period-color relations
do not exist in the Stroemgren system, which is due to the large scatter that
is brought about by evolutionary effects when the uvby bandpasses are used,
they also reveal that such scatter can be almost completely taken into account
by incorporating Stroemgren pseudo-color [C_0 = (u-v)_0 - (v-b)_0] terms into
those equations, thus leading to tight period-luminosity-{\em pseudo}-color
(PLpsC) and period-color-{\em pseudo}-color (PCpsC) relations. We provide the
latter in the form of analytical fits, so that they can be applied with high
precision even in the case of field stars. In view of the very small
sensitivity of C_0 to interstellar reddening, our PLpsC and PCpsC relations
should be especially useful for the derivation of high-precision distance and
reddening values. In this sense, we carry out a first application of our
relations to field RR Lyrae stars, finding evidence that the stars RR Lyr, SU
Dra, and SS Leo -- but not SV Hya -- are somewhat overluminous (by amounts
ranging from ~0.05 to 0.20 mag in y, and thus V) with respect to the average
for other RR Lyrae stars of similar metallicity.
