Hi, Tim, Thank you for your question. First of all, since you are using a planter box, it is best to use a good potting soil. A planter box is a container, and potting soil is best for containers. It is more lightweight and will drain better.   Recognize that if you put a perennial vine in a container, it will probably need to be protected in the winter, as the roots will get colder in the planter box than they would if planted in the ground. This means wrapping the planter box in in bubble wrap and securing it with twine after we have had a freeze. It will also be good to mulch your vine in late November or early December with some evergreen boughs or shredded wood mulch, again to protect those roots. Also, be sure to water your vine in the winter when we have not had rain or snow for a couple of weeks, when the temperature is above freezing, and the soil is not frozen so that it can take up the water. Being in a planter, again, it will dry out more quickly than it would in the soil. With all of that said, here are some perennial vines that will work in a full-sun exposure:

Trumpet honeysuckle, Lonicira sempervirems, is a rapid growing deciduous vine that displays very showy coral pink flowers all season, and their bluish-green leaves provide nice contrast.

Flowering clematis have large flowers, which come in many colors. They are deciduous and grow vigorously when provided with a bit of root protection. (mulch)  (The rule for clematis is "head in the sun, feet in the shade".) 

Silver lace vine, Polygonum aubertii, is a rapid-growing deciduous vine that displays masses of white flowers summer through fall. It is a vigorous grower.  

Scarlet runner bean, Phaseolus coccineus, is an annual vine. It puts out bright scarlet flowers all summer and will rapidly cover a trellis. It’s available in pink and white varieties.

Hyacinth bean, Dolichos lablab, is also an annual vine. Its purplish leaves blend well with its spikes of showy purple or white flowers. It, too, is a rapid grower.

If you enjoy home brewing, you might want to try a Common Hop vine (Humulus lupulus).  It is fast-growing, and can be an annual or perennial, depending upon growing conditions.  It tolerates both low humidity and wind, and in the summer female plants  produce greenish-yellow pinecone-like flowers.  

Trumpet vine (Campsis radicans) or Hummingbird vine (common name) has orange-scarlet trumpet-shaped blossoms in summer at a time that other vines have finished blooming.  The colorful blossoms are magnets for hummingbirds and sphinx moths.  Trumpet vine is another quick grower (are you seeing a thread here ?) and easily anchors itself to trellises, poles, fences, etc. with aerial roots called holdfasts. Flowers bloom on new growth every year so don't be afraid to prune it.   

Most vines, as you read, are vigorous growers and will need pruning to make them behave. 

Here is a link to a CSU Extension PlantTalk article on Vines for Colorado:  https://planttalk.colostate.edu/topics/trees-shrubs-vines/1727-vines-colorado/

Best of luck growing your vine !