I'm not often surprised anymore by whitish or light-toned materials near a rover since Spirit uncovered all that whitish silica with its dragging dead front wheel, all those years ago. It seems we often find that Mars is red only until you literally scratch the surface.
I have to say that Percy often drives right past plenty of rocks I'd like to investigate more. I know that Ken Farley et al. are doing just that with remote sensing (the results of which we aren't privy to for quite a while), so they have some idea of what they're looking at, but I'm often tantalized by a lot of this stuff.