I always enjoy anthracite or obsidian if you want a shiny black and ninja black is nicely evocative if not actually descriptive
Having being hearing woodpeckers all week and at times not catching a snifter of a glimpse think ninja may be an appropriate word here ... having a bit more sympathy than previously for the 'Ivory bill Woodpecker' searchers in the states ...
(Mind you I'm making no effort to physically track them down or get closer)
It's a fortuitous location I think in some respects. Just wish the garden was a bit wilder/more habo but a small range of trees from large conifer to a couple small silver birch and Fig, along with the pond certainly helps, as does being surrounded by other gardens and with reasonable views.Sounds like a decently birdy garden your folks have - enjoying your updates