You could get an electrician.
This is most likely a sub-panel, and can be shut off at the main panel to work around it. But if you have no experience with electrical, get someone who does.
The stud color is fine, as long as it is not deteriorated, it can be purple with no issues.
This will be a tricky spot and you will need to secure it as soon as possible when you remove the old plaster.
Don't worry, your going to be OK. Just a small, but unsafe hurdle.