J-PLUS and S-PLUS (r − J0660) vs. (r − i) colour–colour diagram, equivalent to IPHAS (r′− H α) vs. (r′ − i′). The big yellow and green stars with error-bars are the J-PLUS observations for H 4–1 and PNG 135.9+55.9, respectively. Included in the diagrams, there are families of CLOUDY modelled hPNe spanning a range of properties (density map region). Cyan circles represent hPN PNG 135.9+55.9 spectrum from SDSS, DdDM-1 (Kwitter & Henry 1998), NGC 2022, BB-1, H4-1 (Kwitter et al. 2003), and MWC 574 (Pereira & Miranda 2007). Grey diamonds represent H II regions in NGC 55 (Magrini et al. 2017). Red boxes display Munari & Zwitter (2002) and Munari & Jurdana-Šepić (2002) SySt, this group also includes external SySt from NGC 205 (Gonçalves et al. 2015), IC 10 (Gonçalves et al. 2008) and NGC 185 (Gonçalves et al. 2012), and red triangles correspond to IPHAS symbiotic stars (Rodríguez-Flores et al. 2014). Yellow circles correspond to cataclysmic variables (CVs) from SDSS. Orange triangles refer to SDSS star-forming galaxies (SDSS SFGs). SDSS QSOs at different redshift ranges are shown as light blue diamonds, and YSOs from Lupus and Sigma Orionis (Rigliaco et al. 2012; Alcalá et al. 2014) are represented by salmon stars. Blue stars refer to B[e] stars from Lamers et al. (1998). In the inset plot, the synthetic main sequence and giant stars loci from the library of stellar spectral energy distributions (SEDs, Pickles 1998) are represented by the purple and brown symbols, and the loci of white dwarf stars observed by S-PLUS (DR1, Mendes de Oliveira et al. 2019) are represented by the light green symbols. The limiting region applied in the candidate selection is shown by black lines for hPNe. The arrow indicates the reddening vector with A_V ≃ 2 mag. It was estimated by comparing the locus of unreddened models of PNe with the reddened ones.