Thanks folks!
I have ordered replica (copy) tags before, and they were fine.
In this case I had a bought-in ewe who lost a tag just a few days before being sent to the abattoir, so a red tag made most sense anyway. Then I spotted that one of the home-bred ewes needed a tag too, and I wasn't sure if that now needed to be red or yellow.
'tis done now anyway. Thank you!