template_seagrass.json uses a tintindex pretty extensively and kelp.json and kelp_plant.json both reference tinted_cross instead of cross. However, to my knowledge, neither block actually uses biome coloration, so this is either leftover code from development if ever they did actually use it, or they actually do use it in game and I haven't noticed.

Models with these parameters removed are attached - replacing the normal models with these via resource pack produces no discernable difference.