Where in Colorado are you going? If you check this climate table for Breckenridge (Breckenridge, Colorado - Wikipedia, the free encyclopedia
you'll see that the average high during the 3 coldest months of the year (December, January, February) is 32ºF. That is usually measured at the bottom of the mountain. Temperatures on the slopes will be ~5º colder than that, which is on the warm side for winter snowboarding.
As a beginner, you'll want to concentrate on staying dry (because you will be falling in the snow a lot)
Even for a beginner that falls a lot and doesn't have enough endurance to keep moving, an insulated jacket would make you very warm as you were riding. For most people, a (non-cotton) base layer and shell would be enough to stay warm while snowboarding in the mid 20º'sF
You might get chilly on the lift, or on a particularly cloudy, windy day, but that is mother nature's way telling you to shred some more gnar.
Consider using an optional light, cheap mid-layer. I use el-cheapo $10 fleece from Marshall's or sometimes my body armor as my mid layer.
Even on days where it does get cold (like 5ºF at the base of the mountain), your core usually stays pretty warm and it is your extremities and exposed parts that cause you grief (hands, feet, face, head).
I am 5'7" and 175 lbs. 31" waist and I have plenty of room in most medium jackets.