MSX color-color diagram, as defined by Sevenster (2002), including all known and new maser-emitting PNe and candidates, and adopted from Cala et al. (2022). The vertical and horizontal dashed lines separate the diagram into four quadrants, where different types of sources tend to cluster. The filled star and square symbols without source names represent the previously reported maser-emitting PNe and candidates, respectively. These same symbols with source names are the new maser-emitting PNe and candidates, respectively. IRAS 16029–5055, IRAS 17375–2759 and IRAS 19176+1251 are included as PNe (see Section 5.4). Symbols with red color represent sources with WF characteristics.