Diagnostic diagrams of radio sources with z ≤ 0.05 from the sample of Best & Heckman (2012). LERGs are purple open circles, HERGs purple squares, and star-forming galaxies (SF) orange stars. FR0s from Baldi et al. (2018) are marked by black points. Left panel—WISE color–color diagram. LERGs are in the lower-right corner, while the few HERGs are shifted toward redder colors. SF on the left are spread on a wide zone. FR0s mainly fall in the LERG zone. Those with w3 − w2 > 2 and w2 − w1 > 0.1 (open black squares) are excluded by the sample as possible spurious objects. Right panel—D_n4000 vs. L_{1.4 GHz}/M_* diagnostic plane. The majority of FR0s are clustered in the AGN region with D_n4000 ∼ 2. The sources with D_n4000 < 1.8 are rejected as possible star-forming galaxies or BL Lacs.