カスタムも使えるけど、こういうのチマチマやってくしかないのかな

(custom-set-faces
;; custom-set-faces was added by Custom.
;; If you edit it by hand, you could mess it up, so be careful.
;; Your init file should contain only one such instance.
;; If there is more than one, they won't work right.
'(navi2ch-bm-new-unread-face ((t (:foreground "red" :weight bold))))
'(navi2ch-bm-updated-cache-face ((t (:foreground "Navy"))))
'(navi2ch-bm-updated-unread-face ((t (:foreground "DarkOliveGreen")))))