For most people, A/B testing a complex app (non-app websites are a completely different beast) is not economical compared to tackling larger (and hopefully obvious) design problems.
If your product is so well designed and developed that there's literally nothing obvious that you can improve without either 1) isolating changes down to colors or placement, and/or 2) throwing different options at the wall to see what sticks, then I say:
If your product is so well designed and developed that there's literally nothing obvious that you can improve without either 1) isolating changes down to colors or placement, and/or 2) throwing different options at the wall to see what sticks, then I say:
Congratulations.