FWIW currently portage-3.0.12, but I didn't put it in the summary as I expect most or all current portage versions have this bug.
Today I nearly missed an emerge --ask downgrade indicator. I normally investigate all such downgrades with git log to understand why they're happening and if there's any other actions I may need to take as a result, and nearly missing one is... disconcerting.
So I tried to adjust the downgrade indicator color from the apparent default blue using /etc/portage/color.map. But I couldn't find any setting there that changed it.
Eventually I confirmed by adding the underline attribute to all settings in color.map and trying a downgrading emerge --pretend. Unfortunately both the status letters (including the downgrade indicator) and the USE and USEEXPAND sections weren't underlined at all, while parts like the ebuild name/version were underlined, indicating the terminal supported underline and the setting was working for some elements. Thus this bug.
(Further background: My nearly missing the downgrade likely traces to recent kde-konsole changes that make "intense" and "normal" colors the same. I already had to adjust yellow/brown for that. Presumably the default "blue" is "intense/bright" while "darkblue" is not, and now that konsole is displaying blue as dark-blue, on my konsole color-scheme's default black background it's easily missed. Others are having problems with that konsole behavior change as well so it may ultimately be reverted. See https://bugs.kde.org/show_bug.cgi?id=405345#c9 and the complaints below it. Regardless, all colored elements of portage's pretend/ask output need to honor color.map settings so people can change them if they want/need to.)