With the added information, how about just edging the beach area closest to the house with colorful plants? It looks like you could have a colorful semi-circle of plants where your other plantings end. I would think a local nursery could be helpful with the selection of colorful annuals and perennials with colorful leaves that would thrive in those conditions.
I hate to admit this, but I have to make compromises in order to please my neighbours for whom a nice beach is an empty beach. We have been living in this location for the last 16 years and I always tended to let Mother Nature have input in how the beach should look. As a result, my part of the surrounding beach landscape appears to many, let's say, to be out of place!