Colorado is a great place to live, and I highly encourage you to come here. As far as tree work goes its pretty dead right now where I'm at. Both me and my boss (owner of the company I work for) have jobs in the resort industry right now. Most of the folks here, including my self are set on skiing as much as possible in the winter and usually there is too much snow piled up on the ground to work. Although, we have had some wicked wind storms this winter and have worked a day or so every few weeks doing emergency work. The snow is extremely lacking this season.
But I read that you are planning on heading to Boulder and I'm pretty sure they are working year round down there...same goes for Denver.
Good luck on your quest for employment.