A one night stay won't allow much time to see anything, but would allow a short look and perhaps a visit to the Unterlinden Museum.
Assuming there are no strikes, there's a TGV departure from Paris Est at 09:25, arriving Colmar at 11:44 (time 2H:19M, direct). On the return trip, there's a departure from Colmar at 14;16, arriving Paris Est at 16:38 (time 2H:22M, direct). Leaving in the afternoon will give you a bit more time for sightseeing. Of course there are numerous other train departures, many with one change.
I don't know about French train strikes but it's possible that a few trains might still be running, or possibly the strike won't be for the entire day.
If all trains are out of service on the day you want to return to Paris, it would be a good idea to have a "back-up plan". Rome2Rio lists some possibilities.....
- Rideshare
- Bus (FlixBus appears to have one departure per day at 22:20 but it doesn't arrive until the next morning). That would be a tiring journey!
- Car rental - the drive is about 5.5 hours. It would be prudent for each driver to have an International Driver's Permit, which is used in conjunction with your home D.L. IDP's are easily available at any AAA/CAA office for a small fee.