Hey Scott,
There are two common types of sealers to use on tile and stone - topical and penetrating.
A topical sealer seals the entire surface of the tile and grout and with certain products will give it a "wet" look. These are also known as enhancing sealers. These should also not be applied until 14 - 28 days after grouting. Premature application can also negatively affect the appearance.
A penetrating sealer does just what the name implies but it also allows the stone and grout to "breathe". These can be applied 72 hours after grouting and generally will not affect the appearance of the tile or grout.
You need to use a penetrating sealer and one that is not sold as an enhancing sealer. That should prevent the problem.
As they others said: always test first.
My first post! Hope it helps.