Blue on solder joints?

[Sg37]

I have a Farfisa Fast 4 I'm doing some work on and I have accidentally ripped off three wires at some point which control the vibrato light/heavy rocker. A lot of the solder joints on this area of the organ have this shiny blue colour on top -- does anyone know why or what it is? At some point I was hoping to re-solder the wires. Thanks.

[KDirk]

Would guess the blue is permanent marker applied to the solder at the factog during assembly and testing to signify inspection/quality assurance was completed on a given section. Have seen similar in other old electronics (non-organs) when doing repairs. Could slso be notating test points for someone down line in assembly line to probe to verify a particular signal level

[Sg37]

Thanks, that makes sense. I later found some green joints elsewhere too.