About pītala (if that's the word), if this is a formation with the -la suffic (lac) by Pāṇini 5.2.96-99, then the suffix means the same as mat(up), i.e.,  "having yellow."  Would this be an author trying to be precise, meaning that the result of alchemical process "had yellow" rather than actually being yellow?

However, there may be a problem with pīta-la.  Of words that are not -ā stems meaning a part of the body, the list that can have a -la suffix, sidhmādi, includes pitta, but not pīta.   I'm away from my main reference books: is सिध्मादि an आकृतिगण?  If not, then Pāṇini would seem not to allow the formation pīta-la.

My more learned vyākaraṇa colleagues might be able to clarify this point.

Best,
Dominik