NOTE: This was yet another case where I analyzed and implemented an example from https://volotat.github.io/ARC-Game/?task=evaluation%2F27a77e38.json before realizing that it was an evaluation example.
Makes use of a new property “SecondMostUsedColor”.
Ideally “MostUsedColor” would ignore the gray separator, but “SecondMostUsedColor” gets the job done.