While the pistils of most strains will change color and recede by the time a plant is ripe that is not always the case. Some strains will still have all white or mostly white pistils when fully ripe. Matanuska Tundra is an example of a strain where most to all pistils will still be fully white and not receding when the plants are fully ripe.
When it comes to when to harvest, place more stock in trichome color than pistil color.
CANNABINOL (CBN)
Cannabinol is the primary degradation product of THC and increases in concentration with plant age. The concentration of this product in the bud is heavily dependent on the time of harvest. Harvesting the bud at a late stage also means that the concentration of CBN in relation to THC will be higher when compared to the peak of THC production. It is only mildly psychoactive and can cause "fuzzy head", drowsiness, disorientation and sleepiness in the smoker, properties that can be considered unpleasant in nature compared to the clear high of the THC.
But by all means, decide when to harvest based on what you are the most comfortable with.