Train CDG to Colmar

I did this exact connection from CDG to Colmar years ago, at about the same time. My flight was on time so it worked out beautifully, without needing to head into Paris and wasting all of that extra time. If your flight is on time, you'd have plenty of time to make that connection to the train. If you are an hour late, maybe not - might be tight, especially if you have checked bags (I didn't.). I'd want to plan on the train that gets you there in the least amount of time. I booked my train in advance to save a few bucks but I knew I was risking a train ticket if my plane arrived late and I missed the train. Could be you'd be able to change it upon arrival for a later train - not sure, might depend on the fare you buy.

Actually, I took the TGV train to Strasbourg from CDG, then stopped there to look around for a few hours, then took a local train on to Colmar and spent the night there.

There are high-speed TGV trains running directly from CDG to Strasbourg. Once you reach Strasbourg you would connect to one of 42 daily regional trains reaching Colmar in about 30 minutes.
SNCF, France’s national train company, now allows you to book a heavily discounted “Prem’s” ticket in advance and exchange it for a later train up to 30 minutes before the train’s departure time for a fee of €15. You would also need to buy a replacement ticket at its price which is why it may be best to give yourself a buffer of 2.5-3 hours after landing at CDG to take a train departing slightly later for your destination. Obviously getting through CDG in February is normally quicker than May, but 2.5-3 hours should be adequate. The discounted tickets can be bought for as little as €19 on some routes when they first go on sale. So, if you’re going to land at CDG on April 1, for example, you could buy a Prem’s ticket online on January 1 when they first go on sale. You need to buy them straight away as they are limited in number and sell out quickly. You can read about the Prem’s tickets at www.SNCF.com under “All about our fares.”
www.SNCF-connect.com is where you can buy them.

We prefer a different approach when it comes to train tickets adding up to several hundred dollars. If I was going somewhere for which walk-up tickets aren't too expensive (say Rouen) then I wouldn't book in advance. But for your trip for which the advance purchase savings can be significant I would instead spend the arrival day in Paris and go to Colmar the following day. Odds are good you'll be at your hotel somewhere around noon (earlier if you're lucky, later if the flight is delayed or the immigration lines are slow). But you're pretty certain to be in Paris that day with time to stroll around, visit a museum, sit in a cafe. The next morning you are sure to catch your trains to Strasbourg and on to Colmar.

In April I rode SNCF from CdG to Strasbourg and return to Gare de l'est. Finding the SNCF station in the big airport is easier if you have a map. Trains start loading about 20 minutes in advance. You will have a reserved seat but that doesn't guarantee space for your luggage. The trains can be crowded. The only tip I learned was that there was a little luggage space in the centre of some cars as well as at the ends of the coach. That space was marked by a tag hanging off the luggage shelves above the seats.
PS: As well as its picturesque history, Strasbourg has opened an ambitious contemporary arts museum in the city core.

I also was there in October, I took the SCNF from Strasbourg to Gare de L'Est, not Gare Lyon. Booked online, first class tickets were very cheap. And the train to Colmar is frequent and only 30 minutes. But Strasbourg is so pretty too. Sigh.