Reddening corrected two-color diagrams and unreddened CMDs for NGC 339 (upper panels) and its surrounding field stars (lower panels). Left panels: stars having photometry in vby filters (black points); stars excluded from metallicity determination (open squares); stars used to calculate the mean metallicity of a cluster and field (color-coded points, where colors represent metallicity distribution); lines of constant metallicity (dashed lines); additional selection criteria drawn after visual inspection of the plot (dotted line); obtained mean metallicities of cluster and field stars (black solid lines); the statistical and systematic errors of the mean metallicity of the cluster (darker and lighter shaded areas). The arrows indicate the reddening vectors. Right panels: Dartmouth and Padova best-fitting isochrones (gray and turquoise dashed lines, respectively) superimposed onto the field CMD, in order to illustrate the position of the cluster against field stars.