M 33 galaxy star cluster sample of 161 objects from catalog of San Roman et al. (2010) (circles and stars) and the studied sample of 40 objects (stars) common to Ma (2012) and San Roman et al. (2009). Panels show a) U − B vs. B − V, and b) U − V vs. R − I diagrams. The model grid (without extinction) used to derive physical parameters of clusters is displayed in the background with indicated reddening vectors following the LMC extinction law. The continuous line traces PADOVA SSP of Z = 0.008. The B band magnitudes of clusters were shifted by 0.1 mag.