Optical-to-near-infrared colour-magnitude diagrams of our β Pictoris stars and common proper-motion companion candidates. In both panels, blue filled circles mark bona fide moving group members with membership flag 1 in Table A.1 (see Sect. 2.1), and open circles indicate other member candidates with flags 2 and 3. Black filled squares denote companions previously known in the literature that had not been reported as belonging to β Pictoris. Red filled stars mark our eight new proper motion companions. Typical error bars are shown in the bottom left corner. The black solid line is the average β Pictoris sequence computed with all candidate members as in the left panel (flags 1, 2, and 3). Left panel: M_B vs. B−K_s diagram. The dash-dotted lines are the β Pictoris sequence shifted by ± 3σ. Grey times (×) and crosses (+) indicate discarded companion candidates from astrometry and photometry, respectively; squared symbols mark companion candidates in the WDS. Right panel: M_V vs. V−K_s diagram. The blue dotted line is the sequence with only bona fide members (flag 1). Red dashed and dash-dotted lines are the 20 and 100 Ma isochrones from Baraffe et al. (2015). Green long dashed line is the 20 Ma isochrone from Siess et al. (2000) plotted only at highest masses. For clarity, we do not draw the discarded companion candidates. Some remarkable stars do not have V photometry.