Travel From Rome to Colmar, France

Fly Easyjet Switzerland from Rome FCO to EuroAirport in Basel (about 1.5 hrs). Then train to Colmar (about 45 min train journey).
The train only option is over 9 hours with a minimum of 2 train changes (Milan C.le and Basel).
These are the choices, you decide.

You can see the schedule at www.bahn.com
You could buy tickets from Rome to Basel at www.trenitalia.com or at www.sbb.ch/en. Trenitalia will only show you the direct trains from Milan to Basel, but might have a better price. Basel to Colmar is just a local ticket. SBB might get you a through ticket, possibly at a higher price.
Also check www.trainline.eu. They still don't handle Swiss tickets, but Milan to Basel counts as an Italian ticket and Basel to Colmar is a French ticket.

PS - Looks like the fastest train connection is to depart Rome Termini 8:00 am and get to Colmar at 4:35 pm with connections in Milan and Basel.

It seems like the simplest way to do it is with a 9 hour rail journey. If you go to the Deutsche Bahn website, you’ll be able to see available trains. Depending on when you leave, you can change trains as few as twice or as many as 4 times.

Agree with Roberto, fly!

FCO-BSL...1 hr35m prices start at around €60 Easyjet has one flight/day.

Train takes between 45 min -1 hr 07 min.

2 people decide to have a race from Rome Termini to Colmar

Person 1 takes the 8 am Frecciarosso to Milano Centrale, arriving at 10.59 and changes to the 11:23 EC train to Basel SBB, arriving at 15:29, and changes to the 15:51 TER to Colmar arriving at 16:35. 8 hours and 35 minute journey.

Person 2 takes the 8:05 am Leonardo Express to Rome FCO airport, arriving at 8:37, checks in at EasyJet. Check bags, go through security, walk to the gate and board EasyJet flight to Basel departing at 10:10, arriving at Basel Euro-Airport at 11:45. Get off the plane, pickup luggage at the luggage carousel and walk outside. Take the 12:35 Distribus to St Louis station, arriving at 12:45, and then getting the 13:30 TER to Colmar arriving at 14:05. 6 Hour journey.

The air passenger will get there 2 1/2 sooner. But it is not exactly a no-brainer. There are a lot more processes to deal with flying.

oooh, very well put, Sam! It makes it an interesting question.