Do you know of a perennial vine ( green preferable and stays green year round) that can grow year round in the Baltimore area?
Baltimore County Maryland
You did not mention the site conditions and location - sun or shade. We do not have recommendations for an evergreen vine.
If you want privacy year round, that points to an evergreen, but typical evergreen vines sold in Maryland are highly invasive. Avoid English ivy or wintercreeper. Both spread by berries into wild and natural areas. Also, your choice will very much be dependent upon how much weight your system can support. Some vines get extremely heavy and woody.
These vines are deciduous.
For full sun consider native Lonicera sempervirens, trumpet or coral honeysuckle
Gelsemium sempervirens, Carolina jasmine (may be semi evergreen in a mild winter.)
Full sun to part shade - native Clematis virginiana, virgin's bower;
There are more native choices in the online pub, "Native Plants for Wildlife Habitat and Conservation Landscaping: Chesapeake Bay Watershed." It's a great resource and has photos. https://www.fws.gov/Chesapeakebay/pdf/NativePlantsforWildlifeHabitatandConservationLandscaping.pdf