Thanks all for suggestions. So far a product called "Acu-Shield" sounds
like a potential solution http://www.energysealcoatings.com ; apparently
it can be colored with universal tint. It doesn't sound nearly as messy
to put on as the various Henry's -type asphalt coatings, and it'll stand
foot traffic because it's made for commercial bldg roofs where they need
to service HVAC equipment, etc.
Homeowners assoc, yes, but even if there wasn't, I want to be
considerate of the neighbors up the hill, I'd go bonkers looking down at
a glaring white roof in a sea of PacNW evergreen trees. No heat problem
considering this is just a carport, either.