I've grown purple strains before, it is the anthocyanins of the plant reflecting and leaching into the trichomes, they will still amber up.
Just keep an eye on it, should be starting to amber up in due time.
Good Luck!
Hello, I see differt type of purple strains, some of them show an amber final trichomes and some show a purple color inside. So i think that you can expect to see their trichomes become amber or violet at the end.
Good luck.