i agree that there is a "legibility" issue. the game doesn't communicate the state of unlocked hexes or the rules of how the threshold to lock hexes. It wouldn't necessarily need to be numeric indicator. it could be a visual indicator on a hex to communicate that a hex will lock to a particular colour next turn. For even more usability, the game UI could update these indicators for all hexes when the player hovers over a hex (if you place here, then this is the immediate result you will get..)

Thanks! I did think about numeric indicators but didn't want to introduce too much complexity. Would also take away from the fun if players had to check the numbers for many cells each turn.

Still trying to figure out the best way to show that information.

Maybe some kind of vertical line through the hex, say green on left, blue on the right, and as the line moves away from the middle it's obvious which side is gaining influence there? When it hits one side or the other, it's locked.

Maybe press-hold TAB view them, like the production markers on tiles in Civ 4

That's a good idea! For those on mobile though, perhaps a button to toggle the view?

Or something time based, pulsating perhaps every few seconds as very faint overlay text?

Yeah I agree, but maybe have also non-numbers as an extra option.

very nice game, will pass it around to fellow-go players