Good ways to indictate that a graph applies to a certain feature/person/category

I have a graph with, let’s say, multiple body measurements over time. This graph can apply to one of a few persons, say Peter, Paul or Maria. I have a radio box to select betweebn the three persons and teh graph is updated accordingly. So far so good.

I would like a clear, but somewhat subtle visual way to make obvious that: “This graph applies now to Peter.” The radio button state feels to me like not enough as an indication to the user.

I have experimented with a huge grey text annotation (size=90!) over the whole graph with an opacity of 0.5. (I played even with textangle=45 - which gives you the “draft” look…)

This looks ok, but I would like to ask: What do others to identify a graph as applicable to a certain feature/person/category?