  We present a theoretical investigation of the phenomenon of
electromagnetically induced absorption (EIA) in a 4-level system consisting of
vee and ladder subsystems. The four levels are coupled using one weak probe
field, and two strong control fields. We consider an experimental realization
using energy levels of Rb. This necessitates dealing with different conditions
of wavelength mismatch---near-perfect match where all three wavelengths are
approximately equal; partial mismatch where the wavelength of one control field
is less than the other fields; and complete mismatch where all three
wavelengths are unequal. We present probe absorption profiles with Doppler
averaging at room temperature to account for experiments in a room temperature
Rb vapor cell. Our analysis shows that EIA resonances can be studied using
Rydberg states excited with diode lasers.
