A new visual -- near-infrared diagnostic to estimate the metallicity of cluster and field dwarf stars Annalisa Calamida (OAR-INAF), M. Monelli, A. P. Milone (IAC), G. Bono (Univ. Tor Vergata), A. Pietrinferni (OACTe-INAF), E. P. Lagioia (U…