Dear Andrea:
Quite frankly I'm kinda baffled. I never even heard of such a thing. So I will only try to guess, assuming that it is a recent installation (you don't say). Ubatuba is green; if the installer used say a yellow-colored glue (Liquid Nail™, maybe), it may be wicking up from the bottom and the side of the faucet hole, and create a bluish discoloration (yellow and green make blue).
But while it may make sense, it is just a wild guess due to lack of better information.
May I ask you now to please read and e-sign our Statement of Purpose at:
http://www.marblecleaning.org/purpose.htm?
Ciao and good luck,
Mauri
Article ID: 1292
Created On: Mon, Mar 3, 2008 at 3:44 PM
Last Updated On: Mon, Mar 3, 2008 at 12:00 AM
Authored by: Maurizio Bertoli [mail@mbstone.com]
Online URL: https://marblecleaning.org/knowledgebase/article.php?id=1292