I think NPC nameplates should be much bigger in font size and a color that isn't black-- as more often than not it usually blends in with the background. Another suggestion as well for NPCs looking left or right their nameplates seem to be further above their heads.
A personal suggestion would be to make them gold or some yellow. Though that isn't always a perfect fit. Maybe a bright green? Or perhaps a nameplate behind the name to highlight it regardless of background.