I would like to prevent flyspell from changing the foreground color of words, and just add a red underline.
I've tried the suggestions here, but it doesn't have any effect: How to overlay a face in Emacs that ONLY modifies the underline. Perhaps I'm missunderstanding the answer, but setting inherit: undefined in the customize interface does nothing.
Guessing I should customize flyspell-duplicate and flyspell-incorrect, but how?
As suggested by @chakravarthy-raghunandan the issue was with a local customization.
Turns out the theme I'm using set this, so my customizations were overwritten.
Putting this in my init.el fixed the issue:
(custom-theme-set-faces
'cyberpunk
'(flyspell-duplicate ((t (:weight bold :underline (:color "#ff0000" :style wave)))))
'(flyspell-incorrect ((t (:weight bold :underline (:color "#ff0000" :style wave))))))