Changing Default Highlight Colour

Is it possible to change the default Highlight colour from yellow to one of the other options e.g. pink. At the moment you seem to have to select say pink at the start of a session before it will stay pink but it will revert to yellow again when you restart Scrivener?

No, that is not something you can do, presently. As you say, it will stick for a session but after that you have to reset it again.