Vintage 1960s Shift Dress

Channel Jackie O in this charming 1960s pink and white shift dress. Canadian union tag but no size/composition tag. I’m marking this size small but it’s a relaxed fit and should work up to size M. I wore this dress to a couple of parties and got so many compliments! See in photos one small dark mark on the back but I can’t tell if this is damage or in the original fabric.