Man pages matching name bitmap_mask_color in section 3alleg4:

bitmap_mask_color.3alleg4.en	debian 10 / allegro4-doc
bitmap_mask_color.3alleg4.en	debian 11 / allegro4-doc
bitmap_mask_color.3alleg4.en	debian 12 / allegro4-doc
bitmap_mask_color.3alleg4.en	debian 13 / allegro4-doc