So, biomes in Minecraft have two color values for water, waterColor and waterFogColor. Every single Vanilla biome uses different colors for the fog and the water surface color. However, without editing the code, MCreator biomes use the same color for both the water surface and fog, which, though small, is quite noticeable when swimming between biomes or something. I'm just simply asking for a second water color value, setting the water fog color.
Though I don't have the slightest clue how, I imagine it would be pretty easy to add this feature, because, again, there are two clear values, "waterColor" and "waterFogColor" (using decimal color codes) which can be changed in the code easily.