We present new empirical and theoretical calibrations of two photometric metallicity indices based on Walraven photometry .
The empirical calibration relies on a sample of 48 Cepheids for which iron abundances based on high resolution spectra are available in the literature .
They cover a broad range in metal abundance ( -0.5 \leq [ Fe/H ] \leq +0.5 ) and the intrinsic accuracy of the Metallicity Index Color ( MIC ) relations is better than 0.2 dex .
The theoretical calibration relies on a homogeneous set of scaled-solar evolutionary tracks for intermediate-mass stars and on pulsation predictions concerning the topology of the instability strip .
The metal content of the adopted evolutionary tracks ranges from Z = 0.001 to Z = 0.03 and the intrinsic accuracy of the MIC relations is better than 0.1 dex .