By definition no.4 heroin is hcl and not base, if it is base then again by definition it is no.3.
With that said, "China white" is generally not diamorphine, it is fentanyl or an analog, and it has nothing to do with being cut by dealers, it was manufactured this way, and I guarantee there is plenty of it floating around down under.
But its just slang, anyone can use it to describe anything they want, perhaps you are using to describe heroin hcl that is very light in color. I've seen plenty of white heroin, or off-white, and this is over a decade ago before fent had hit the scene; and sometimes people called it china white, but the term wasn't as prevalent as it is now, and if I hear someone use it now I assume they are describing fentanyl or an analog whether they are aware of it or not. Nowadays when people say china white the "dope" that goes with it is bright fucking white and obviously not real heroin, whereas before it was just used to describe real dope that was whitish in color. That's not to say all fent-a-dope is white; it all depends on what it is cut with.
Perhaps in Australia the situation is more like it was in the US a decade ago, but I would try to avoid using slang whenever possible, especially on the internet where regional slang will lose its meaning.
