Clap 4: bold & underline rather than color

I just switched from clap 3 to 4 and although I can see that the textual presentation is better than before, the highlighting is bold and underline rather than color. (I'm using Xubuntu 20.04 with an Xfce Xterm.)

Is it possible to go back to colors?

That's not possible afaik. According to the release announcement they plan to make the colors customizable in future 4.x releases, see clap 4.0, a Rust CLI argument parser

Ah, thank you, and also for the link. Unfortunately the linked page mentions a migration guide but doesn't seem to provide a link to it!

The migration guide is part of the change log.