  We present two-color modulation transfer spectroscopy as a tool for precision
studies of atomic properties of excited states. The bi-colored technique
addresses a narrow set of velocity groups of a thermal atomic vapour using a
two-step transition to "burn a hole" in the velocity distribution. The
resulting spectrum presents sub-Doppler linewidths, good signal to noise ratio
and the trademark sidebands that work as an in situ ruler for the energy
spacing between atomic resonances. The spectra obtained can be used for
different applications such as measurements of energy splittings or
stabilization of laser frequencies to excited atomic transitions.
