General question: why did you specify --aura-red instead of --vaadin-red?

My assumption would have been like this: I can re-use those variables inside my theme that extends aura - meaning I would always have to remember that they are named --aura instead of --vaadin like everything else. This also comes with the problem that I can't switch e.g. between aura and another theme you create in the future, which might use --lorem? (I know there is --lumo.. but this feels like a deprecated thing.. or?)

The only/main reason because these properties are defined by the Aura theme.

Now I wonder if there’s any benefit in having separate prefixes in different themes? Maybe all themes should just use --vaadin? I mean, you’re never supposed to use/extend more than one theme at a time.

That would leave the existing Lumo properties in a weird place, though.

Lumo is "deprecated" anyway, or? I would vote for --vaadin, but that's up for you and the others to decide :) from a user's perspective it feels "better" to only remember --vaadin regardless of which theme we use

Lumo isn't entirely deprecated. The shadow DOM implementation is. We are planning on refactoring/rewriting it in 25 minors from shadow DOM styles to light DOM. That could be a place where we rename the properties as well.

I agree, it would be nice to have just a single namespace for these. Somehow it just feels academically correct to have a theme-specific prefix.

IMO the problem is also that if we had theme-specific properties called --vaadin-something, that are available in Aura but not in Lumo, you'd have to know/remember/lookup which are available in which theme.

That might sound stupid.. but with "AI rising" it probably might even be good for those nifty LLMs that all properties (independently from the used theme) use the same prefix.. not just for humans / developer 😅

If it’s mostly about the palette, perhaps we can consider moving those to base styles eventually. Or did you already consider some other Aura-specific properties, which you’d want to use in another theme?

I have not looked into all properties in detail, my gut feeling would be: all public properties should be prefixed with vaadin. all "internal" properties should be either aura or something else