I'm wondering about that myself...it doesn't sound like anyone's found out yet. You don't even have to go as far as lying with someone, you can make smaller amounts by doing things like holding hands or embracing, so it's strange that it's become something they can't do. Especially since we've had some visitors before from another part of this world who seemed to need Chroma to raise their young, but needed to come for our help to gather enough this time.