Introducing my LEGO Parts Guide, which is powered by images exported from LDraw.

[tom alphin]

That said I do have a list from 2019 of what LLs could order and you can filter it by "Q-Part", and those are only colours that can be ordered by the LL Builders, out of a total 11000 parts 898 are Q-parts.

And they all have an Element-ID, which is basically their order number.

That is interesting, and it confirms that a specific shape (mould) is not a Q-Part, but rather specific parts in specific colors (aka specific elements) are Q-Parts.