That's actually part of the mod I made for lambsaucer, as they requested that ocean water be blue like pre-1.13. Although, I didn't test how ocean water looks blended with normal water around islands and the like. I'm going to try to make it look better by tinting all biome water around the ocean level, once I figure out how to do that.
In the meantime, here's a version where all water is the original turquoise color, if you would prefer that:
PureBDCraft Original Water Color Only
Edit 1: I figured it out. Literally all I had to do was define the map as a grid format. Oof. Now all biome water (except swamp) in this one is pre-1.13 blue around the sea level, and blends into the light blue water.
PureBDCraft Original Water Color + Deep Blue Ocean Water
Unfortunately, a side effect of this is deep blue rivers. There are usually river biomes around large islands, so untinted river water would result in light blue water splotches around these islands.
Please let me know what you think of this, Lambsaucer. Personally, I think it looks so much better. ^_^
Edit 2: Oh yeah, I forgot that the tweak I made for lambsaucer uses the 64x water textures. Now I've added the water textures from all resolutions to both packages. Though, now the files are too big to be hosted on BDCraft. ^_^;
Edit 3: I've edited the underwater color map and particles as well to match the color of the original BDCraft water, and the pre-1.13 blue ocean water.
PureBDCraft Original Water Color - Underwater.zip
PureBDCraft Deep Blue Ocean Water - Underwater.zip
Sadly, I can't find a way to change the color of those purple "bubbles" with Optifine. They seem to be hardcoded in MC, much like that annoying "blue fog" you see in the background near the surface of ocean water.
You do not have the required permissions to view the files attached to this post.