Frost-proof containers are a must in Colorado. The initial investment might give you pause, but when you think about how easily plastic pots break, it's worth getting pots that can be used year round. Large pots can be anchored with a tall perennial flower or even small shrub, and filled-in with annuals for more color. Draping vines like sweet potato ('Marguerite' in chartreuse green!) provide contrasting color and texture against a jewel-tone container.