The alternative partitive form "vihreätä" is flagged as a typo.
Does the verb "beat" the number? I thought, yksi does not require partitive.
The number does not count, if you pardon the pun. In this case, the verb etsiä practically always takes the partitive, because its aspect is unfinished.
I belive this is because the "one green owl" is the object of an unfinished action. So partitive
This was confusing to me too. I wanted to put it in partitive form, but avoided it since the number one was involved. I guess if even the number is partitive, the thing it refers to must also be?