A way of getting rid of the purple rain is to go to File...Preferences, and reduce the "seconds to remove trail lines" to 1
Problem is that you won't get any trail lines at all, but apparently the trail lines take quite a bit of processor power, so your map display might get smoother!
EDIT - another way to get rid of them is just to turn Hardware flights off for a moment - RB then forgets where they were, and they start growing again when you turn the Hardware flights back on.
Rod