For When it gets really cold, this is what I wear
Bottom
Kuiu Ultra Merino 210 Zip-Offs
Kuiu Kenai Pants or Super down pants. I usually don't need this layer unless it is DAMN COLD.
Favorite Soft Shell Pants. Kuiu Guide or similar
Gaiters if snowy
Hot hands Toe Warmers-My toes get cold and if you are setup in one spot for a morning these help. If you are moving, not needed.
Top
First Lite LLano 1/4 zip
First Lite Chama
Sitka Traverse
Your favorite Puffy here
Softshell-Kuiu Guide or other similar softshell
Others
Sitka Blizzard Beanie for super cold, or just standard orange Under Armour beanie if just cold with an orange ball cap for when it warms up.
When it is super cold, I also have an UA balaclava to protect the neck. In colorado with the orange requirements, I don't find hooded pieces useful if you stay within the letter of the law.
Merino Liner gloves and then a good set of gloves to go over those, or even a muff to keep your hands in. The Merino liner really helps keep your hands intact when you have gloves off to do things.
Handwarmers if needed depending on your glove system.
Cushioned seat- There are tonnes of types out there, but I use NEP Outdoors Heat a Seat. It is just cushioning to sit on and it gets your butt up off the ground a little more than a pad. Only useful if you plan on sitting for a couple hours, but I find it invaluable.
Something like the above should be more than warm enough for what Colorado throws at you and it is overkill if it isn't really cold, ie 30's to 40's and sunny.