I bet there’s a way to have the best of both worlds but just turning it green isn’t the right solution. Even though there are plenty of cases where the goal has intentionally ended, the more common case and the case we care about a lot more, is that you unintentionally let the goal end and so it’s by design that it’s all red and in-your-face to induce you to restart it (or archive it – to make an explicit decision about it one way or another).
I think in the future when the UI ensures that a goal would never have ended in the first place unless you very explicitly wanted it to, we can add fireworks or confetti or whatever instead of a garish red FIN.
(I know this feels like an unsatisfactory answer for the power users here in the forum for whom an ended goal is always absolutely intentional.)
Some relevant principles:
PDP says we won’t throw the intentionally-ended use cases under the bus (not without blogging about it at least! which, to be clear, we have no intention of doing and I have plenty of finite-time Beeminder goals myself, like for reading books)
Egg-Basket Principle says that we don’t care about those use cases as much
Anti-Cranial-Silicosis says we can’t let an ended goal go out of sight out of mind unless we know you explicitly chose for it to end