  The error exponent of the typical random code is defined as the asymptotic
normalized expectation of the logarithm of the probability of error, as opposed
to the traditional definition of the random coding exponent as the normalized
logarithm of the expectation of the probability of error with respect to a
given ensemble of codes. For a certain ensemble of independent codewords, with
a given power spectrum, and a generalized stochastic mismatched decoder, we
characterize the error exponent the typical random codes (TRC) for the colored
Gaussian channel, with emphasis on the range of low rates, where the TRC error
exponent differs in value from the ordinary random coding error exponent. The
error exponent formula, which is exponentially tight at some range of low
rates, is presented as the maximum of a certain function with respect to one
parameter only (in the spirit of Gallager's formulas) in the case of matched
decoding, and two parameters in the case of mismatched decoding. Several
aspects of the main results are discussed. These include: general properties, a
parametric representation, critical rates, phase transitions, optimal input
spectrum (water pouring), and comparison to the random coding exponent.
