Rule guess: When a White chain touches a Black chain, they must have the same number of liberties.
Do you allow positions that have an unequal number of White stones and Black stones? I guess it would be hard to prove that they cannot occur in a go game, since there could have been captures.
Good guess, but here are (additional) counter-examples:
Yes, I just require that all chains have at least one liberty.
With passes allowed, I believe all such positions can be reached in a normal go game, even without captures. With passes not allowed, that could be an interesting question. But a question for another thread
Hypothesis: White is always in the minority when touching black chains.
More precisely: if you count the stones in a white chain and the stones in all black chains touching this white chain, then either you have counted more black stones than white stones, or the white chain is not touching any black stones at all.