If its an investment for rental I wouldn't be worrying about colour etc. I would concentrate on more of the same and introduce some form, shape, structure, enclosure and possibly screening to the vacant space.

Also don't believe everthing you see in Lowes, alot of that stuff is forced or retarded in specialist polytunnels in a way you could never emulate in low maintenance outdoor environment in late summer. Potted Azaleas will most probably bake and die without a deep leaf litter and moist humusy soil!

Indian Hawthorns (Rhaphiolepis indica) are good value, and flower but deer love them. Pittosporum tobira, Ozmanthus, Crape myrtles are also a good bet along with some palms for architecture. I would get to know the local area and what grows well and lush looking with the minimum of care (What's growing in the central reservations in roads etc.). Hibicus will flower but what will they look like without loads of care on their own....Stringy and weak?

Alternatively you could do a native scheme if it was bold enough. Less is more in my opinion, in terms of different species etc. and its far more impartial and restful - so your tenants are more likely to gel to it.