Hey SmokinJuan,
This is normal and nothing to worry about, different strains have pistils brown at different rates. I have had flower harvested with probably 30% white pistils still but had 30% amber trichs; I have also had flower where the pistils browned very quick in your case, especially with hairy strains but took forever for the trichs to develop. So, in that case I was about 30% amber with all the pistils browned.
Each strain and pheno is different, nothing to worry about brotha!
Cheers,