My dad and I don't share a lot of overlapping taste in clothing, but if you look hard enough you can always find common ground. There are a lot of compelling entries above mine, but this is definitely the ultimate pick for my dad.
Gray is hard only when all you wear are gray pants. Like you, I wear a salt and pepper SC with light, medium, and dark browns and blues, various shades of olive, sage, and army greens, various reds and burgundies, etc.
Relatedly, I'm bumming around I one of my Despos coats (black and white herringbone), sage green cotton Rota pants, and Alden Indys under a navy single breasted Norwegian Rain coat. I look as good as Mr. Six.