Man pages matching name al_color_rgb_to_xyz in section 3alleg5:

al_color_rgb_to_xyz.3alleg5.en	debian 10 / allegro5-doc
al_color_rgb_to_xyz.3alleg5.en	debian 11 / allegro5-doc
al_color_rgb_to_xyz.3alleg5.en	debian 12 / allegro5-doc