Dear Karol:
You don't have a stain, You rather have a “stain”.
A stain – a real stain – is always darker than the stained material. If it is lighter, it's either a mark of corrosion created by an acid (etching), or a caustic mark created by a base (bleaching). There are no known exceptions to this rule. In the case of natural stone, bleaching can't occur, and therefore they are etch-marks all the time: plain and simple surface damages, like shallow chemical scratches.
You should be able to repair that with a good quality polishing compound for marble designed for homeowner and DIYers, like MB-11.
If not, your only option is a reputable stone restoration professional.
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: 1621
Created On: Mon, Aug 11, 2008 at 8:55 AM
Last Updated On: Mon, Aug 11, 2008 at 12:00 AM
Authored by: Maurizio Bertoli [mail@mbstone.com]
Online URL: https://marblecleaning.org/knowledgebase/article.php?id=1621