Using Fabric API 0.19.0 build 398, OptiFabric-v1.4.1 and OptiFine 1.16.2 HD U G3 the custom water colormap that optifine offers does not work. When Fabric API is not installed the custom colors do work as intended.

You can notice the issue with the resource packs bedrock-biome-water and caelesti for example. The file that is supposed to supply these colors is minecraft:optifine/colormap/water.png

I can post the logs (which look normal to me) and settings if you are unable to reproduce the issue.

This will be Indigo overriding the normal fluid rendering not taking OptiFine's changed fluid tinting into account. Hopefully should be quite simple to fix.