Colorado is a year-round destination, so “when to go” depends entirely on what you want to do. Ski season generally begins in late November and you can expect high prices and full hotels during peak seasons (late December, mid-February, and spring break in March). April and May comprise the shoulder season, aka the “mud season,” when ski resorts close down and dude ranches start sprucin’ up. You may be able to find some good deals during this time. After that, the gorgeous mountain summer and fall months take over, when many people book camping trips and it’s generally sunny during the day and cool at night.