First, make sure that when there is something like this that comes up, the issue is with a specific implementation that was outside of your control, not just a directive to "do something". If that is the case, then usually the best response is something along the lines of:
"The decision was made by do xyz. If there are questions or concerns, the best person to bring them up to would by director's name."
If pressed further for more information, then you respond that since you were not the one to make the actual decision, you cannot provide any detail about how the decision was made, since it would be irresponsible to defend or criticize the decision, since you were not a part of the decision making process.
This might come off as passing the buck, but in reality, it is irresponsible to try to provide reasoning for a decision that was made by someone else. If this happens repeatedly, you can always ask your director if there is a reasoning that you could share.
If this is seen as passive aggressive by your director, then in all honesty, there's nothing you can do, since this would really be the most responsible response to make. Ultimately, though, your response has to be 100% that you support that a decision has been made, and that you are implementing that decision to the best of your ability.
Of course, if there is a legal or ethical reason why the decision is wrong, then that would be a different issue. Your question did not indicate that this was the case, though, so this path would probably be your best bet.