How do I change fluid opacity?

I’m using a transparent shader for the fluid domain. Is this the object I need to be adjusting rather than the fluid itself? So, how do I chance the opacity to something more like paint or blood? Thanks

The fluid domain is the object that you assign the material to for the fluid. A pure transparent shader on the domain means you will see nothing. The fluid objects, after baking, “become” the domain object.

You could mix diffuse and glossy with fresnal, and then mix in some red glass, or you could use subsurface/transmission on the new and completely awesome principled shader.

Glossy and Diffuse mixed together will give you a basic plastic/paint/shiny material.

Glossy and Transparent mixed together will give you a basic glass-like material.