The fungus is an ever-adaptive being, gathering flaws, studies and observations from each body that returns to it, seeking more ways to improve, to strengthen, and to mimic.
Across versions, subtle changes are made to the fruits that are grown out of it as per the aforementioned observations.
A new version is considered once a significant change is discovered that defines the way the fruits are grown (e.g. all iterations of Mužmir Amanita I had caps that were formed the right side up).
The Mužmir we know now is Mužmir Amanita III - and even within just its own version, there are countless iterations fine-tuning what it has found over decades, if not longer.
Color vision and the addition of 'lungs' were the main significant changes between II and III. The rest of his humanoid appearance is thanks to years and years of constant subtle improvements.

In all likelihood, the first iteration of Mužmir IV would be the first fruit that figures out how to see the color red in an efficient manner.