Depends on what you are used to. Yeah you can wear a sundress, you might get little goosebumps if the wind blows your way. Its chilly but if there is sun it would feel a little fresh, if there isnt, it would feel a little cooler than fresh. And if you live in a place where there is snow a lot, 68 could be considered warm or nice for your usual climate.
A little too brisk indeed as SaVes has pointed out, its a bit chilly. I wouldn't recommend wearing a sundress haha. But it does depend also on your adaptation to temperature. If you're used to really cold weather, 68F will be quite pleasant.
"Depends on your temperature tolerance" is what I would say but then I thought to myself "You don't actually know your own temperature tolerance and you have been alive for a fifth of a century. This is frivolous."