Superficially, it says what it is, which is a Framework Of Skills for Inquiry Learning.
However, the fact that it also sounds like FOSSIL is deliberate. Firstly, the discipline of archaeology seems to me to be a particularly helpful way to think about inquiry, and to explain it, especially to children, although I have not developed this idea further. Secondly, it serves as a warning against complacency, because a framework, or progression, of inquiry skills, an increasing number of which are dependent on digital age technologies, must evolve in response to changes in the environment if it is to remain vital.
A fair deal of thoughtful reading went into choosing the colours of the stages.
I am no expert, and had I had longer I almost certainly could have done better, but I tried to choose for each stage the colour that appeared to be most closely associated with the kind of activity involved in that stage. So while the choice of colour for each stage is somewhat subjective, it is not entirely random.