You don’t always know. I pair things up based on either the genetic background of the gecko for certain traits, or for the physical expression of a trait that the gecko is showing. For example, this year I paired ember with basil because they are my most concentrated orange/red male/female. So far their babies are great. But I was thinking about pairing ember with applejack next year because while applejack isn’t red at all, he comes from a red line and is my largest female. Absolutely monstrous compared to the rest and since ember is my biggest female, maybe they would make giant babies. Some of my geckos have moderate amounts of white, but they have siblings with insane amounts so I try to pair those together on the chance of getting a high white baby. It’s all variable and based on personal preferences.