For the most part pistils will turn an orange, brown, pink, red, yellow or purple color. Some strains keep producing white pistils until you chop it. So it may never seem ripe, but it very well may be ready to harvest.
Well right now they are 4 weeks and 1 day into flower, so no harvest yet. I'm also wondering how to gauge when to harvest? I know the trichomes method but I saw someone else post about pistil hairs