Figuring out ground in AC circuit
The case is dangerous! Wrong connections or materials can cause dangers and invalidate insurances. Even electric works done by non-qualified persons can invalidate insurances.

There's no evidence are old wires connected as the code stated in the assembling day. More: You probably do not know the valid assembly day code.

Where I live the code has allowed as late as 20 years ago color variations if the wires were labeled. The labels can be taken off and as well the electrician can have decided "not enough that right color, but I use the other - who cares - time is money and other works wait!"

Do not make more unorthodox connections - get qualified local help or find the other ends of the wires!