Very good - on underlining links
We shouldn’t rely on colour alone to indicate that something is interactive.
Take links, for example. Sure, you can give them a different colour to the surrounding text, but you shouldn’t stop there. Make sure there’s something else that distinguishes them. You could make them bold. Or you could stick with the well-understood convention of underlying links.
---- Also see https://adactio.com/journal/22085 follow up for underline and line-height with the unit lh.