meta name=theme-color isn’t the embed color, it’s used for theming in the browser
See this: https://developer.mozilla.org/en-US/docs/Web/HTML/Element/meta/name/theme-color
oh i don’t have vivaldi to test and wasteof isn’t a pwa, but i’m sure it had a theme colour last time i checked
also, theme-color is the embed colour, though it's possible another one may be used for that too
I just tested in safari, it has a theme color but it’s like gray, I think it’s auto chosen because there’s not an actual meta element