I prefer looking at the bud structure as a whole. Colour of pistils doesn't mean much as I've had plants that brown at week five, but dont recede and swell until week 10. I'd wait for the pistils to loop back into the calyx and wait for the calyx to swell soon after.
Assessing trichome colour, bud structure and pistil receding/calyx swell as a whole is more reliable.
You will also notice a ripe bud has a milky, silver haze from a distance. I find that overall colouring more reliable than a close up of trichs strangely.