Just switch the System Appearance to graphite instead of blue.
Traces of the original Plaster were left untouched in the blue version for reference sake, but also for people who like round elements better.
This works for both PlasterAGV and PlasterSTYL.
BTW, probably the only real difference between these themes, apart from their creation dates, are the Mail and Safari skins using folder icons from Serenity / deSTYL.