Pb-based pigments and rhodizonate salts
According to Ashley et al, "a rhodizonate spot test kit [for] in-situ testing of lead in paint... can be used for screening (i.e., qualitative) purposes." The test is sensitive not only to metallic (elemental) lead, but also to lead compounds used as pigments. However, the reference cited also states that the sulfide and rhodizonate tests have a high incidence of false positives.

Sodium, potassium or even cesium salts of rhodizonic acid should be equally effective, since the active species is the rhodizonate ion, but be aware that the sodium salt is less stable in water solution and should be used within a few days.