Hilchos Lashon Hara, chapter 2, section 2

When we find that Chazal permit lashon hara “before three,” this relates to saying something that is not an outright denigration and is ambiguous. Something like this depends on the speaker’s tone of voice when he talks. If he relates something like this before three people it is permitted, because since he knows that his words will certainly reach the ears of the person spoken of, he speaks in a positive way.