We introduce stepwise resonant excitation by two-color optical near fields in order to detect Rb atoms with a slit-type detector. Blue fluorescence of the second D2 line is monitored for background-free detection. Feasibility of the method is shown from an experiment with a Rb vapor cell, where a sub-Doppler spectrum with the FWHM of 80 MHz is obtained. The detection efficiency is estimated at about 3% for cold Rb atoms.