This is actually a bug in Camera Mode that’s existed for quite some time; I’m a bit surprised it hasn’t been fixed yet. It affects other biomes, too. Namely, only half-block waterfalls change color to match the biome/water fountain in Camera Mode; the actual bodies of water remain default blue. Also, the water’s overlap with the half-block itself is not rendered properly.
A temporary solution is to place down a Pure Water Fountain, so the waterfall’s color will at least match.