6 Days Trip Help me plan Switzerland, Lake Como and Colmar France

Seeing those places in 6 days is going to take up all your 6 days, so you have your answer. Stay in Colmar & on Lake Como. If you’re flying back out of Zurich again, that’s going to be a lot to fit into 6 days in my opinion, but can be done if you want to use up 2 of your 6 days traveling.

Doable, but transportation heavy and not much time to enjoy any of the three locations.

How about fly into Zurich, 1 day in Lucerne, 1 day in Zermatt, 1 day in Lake Como, 2 day in Colar, France?

which of those nights will you be where? Is a "day" followed by travel or is that next day?

If you're in Lake Como, particularly Varenna, you could fly out on Milan instead of Zurich. It's a multi-city, (open jaw) ticket.
Safe travels!

for those saying an out and back is too much in a day, just to say my wife and I did it. We stayed near Chur and using Regional trains went all the way to Tirano and back with a stopover in St Moritz (recommendation - it wasn't worth it) with time left over.

We drove from England (our own car) on our usual trip and spent a week visiting railways and villages and towns all over the Engadine, including the day down to Tirano and back.

I suggest you start here https://www.rome2rio.com/ to get an understanding of how long it takes to travel between your desired locations. You can then budget your time accordingly.

With your plan of 1 day in Lucerne, 1 day in Zermatt, 1 day in Lake Como, 2 day in Colmar, at minimum half of your days are going to be taken up with travel getting between all of these places, so it’s more like “a late afternoon/evening” in each place. I strongly recommend you skip Lake Como and do something like 3 nights Luzern & 3 nights Colman or 2 nights Luzern, 2 nights Zermatt & 2 nights Colmar. Or if Lake Como is a non negotiable than just do Como & Colmar and skip your other stops.