The only mention of a Green in Ayr is a street of that name.

In Skerringtoun there I was born
And in Loudon I was dwelling.

We certainly have a Skerringtoun [the farm of Skerrington Mains still exists in the parish of Loudon. In my youth it was farmed by the late Willie Young] but tell me where do you find a Scarlet Town and indeed Loudon is only one letter different from London. Could someone have misheard or misread in this case?

To muddy the waters still further the site of Auchruglen Castle, supposed by some to be the scene of the tragedy expounded in the ballad "Edom O Gordon", is also in the parish of Loudon.

[Note] Mains usually denotes the Main or Home farm of an estate.