  Fast spectral variability of gamma-ray burst emission is considered for a
number of events seen by the Konus-Wind experiment. The variability manifests
itself as a strong correlation between instantaneous energy flux $F$ and peak
energy $E_p$. In the ($F,E_p$) plane, the correlation produces distinct tracks
in the form of branches and loops representing the different parts of a burst
time history. Despite the variety of features seen in different events, the
main characteristics of the spectral evolution produce a quite consistent
pattern.
