What works out really well is turning a flag halfway but not turning it yellow. You have to run at exactly the right time, but it can definitely be good. 1, you don't give them a yellow. 2, it literally is the same color so unless they remember that you did it or randomly mouse over it they can't notice. 3, when you go back it'll change instantly and they'll be like "wtf!!" There are definitely times that I will forget a portal flag was turned almost halfway.. then the next time they go in, it changes and nobody can port. I've also used this against other people.
Very interesting and helpful, thank you!
You turn it yellow, which is definitely noticeable if they ever look at the minimap.
That's why I said it's only useful end-game in minimal player settings (1v1, maybe marginally 2v2). Also, it tends to work best on flag clusters that kind of merge one into the other on the mini-map. That said, I'm sure it doesn't work in super-pro games.
BTW, I have recently seen two replays involving you, Orcun, Hedgie, Thundercles, Darkliath and Nomilarac... Something like TB-Reg-Sed mirrors. I don't think you guys make mistakes at all (though in the second game Hedgie's Sedna charged right into towers for some reason: he must have lost control of the mouse or something, it couldn't be a deliberate move), except very tiny ones that get immediately exploited by the opposing team to the fullest. That's all extremely professional and has a great educational value for newbie players like me, but a tiny question arises: isn't playing Cataract for bazillionth time a bit boring? After all, even I can already draw an algorithm of skilled game on Cataract for both sides. Demigod is not chess, obviously. And I've yet to see a Zikkurat, Brothers or Mandala game being hosted, for example (though, admittedly, there are some Leviathans, Crucibles and Prisons in the lobby from time to time).