I'll have a look at this later. So far this has been a desired effect on things such as leaves, as shadows pass through them, but I can see you would want to be able to toggle this

Scratch that; all of them are, so this isn't sensibly convertible to the RGB centric shaders, at least not an exact version of Photoshop's implementation

I think those are all, with the exception of Luminosity, based on a HSV model, which is quite expensive to convert back and forth between on a shader level.

Yeah, I've planned to have a override/auto setup in the blend settings as well, because if you manually set it to Additive, for instance, you wouldn't want Alpha/Alpha clipping to override that. Could you open a new topic on that?

Yeah this is a silly issue. It's because clipping is done before the screenspace coords are calculated.