[R] Text in Boxes?

[David Reitter]

It's probably a beginner's question:

How do I show text in boxes?
That is, can I specify a background color for text output with text() ?

The following doesn't work as I would expect:

text(labels="123", 50, 0.5, bg="green")

I've experimented with legend(),which will make the box too wide, and  
also with rect(), which doesn't know the extent of the text shown.

The concrete application for this is are multiple time series shown  
in different colors, and I'd like to show the boxed text (with the  
appropriate colors) right next to (the maximum of) each time series  
in the diagram. Color text is hard to read, so I'd like nice colored  
boxes around black text.

Thanks for your help :)