Is it obligatory for a girl who has had her thyroid gland removed due to a tumor to inform her suitor of all the details of her illness, or is it sufficient to mention the removal of the gland and the use of hormone replacement therapy? And does a difference in skin color between the suitor and the fiancée affect the decision to marry?

If the situation is as described, you are not obligated to inform him about vitiligo, nor is it advisable to do so, because it does not affect enjoyment or pregnancy, is not contagious, and is not considered a defect that requires disclosure. Mentioning it might deter the suitor.

As for the difference in skin color between you and your suitor, there is no harm in it, and it should not be an impediment. What is important is religion and character.