Plants are starting to change color

[NorthernGreener]

Hey guys , my girls have started into preflower and I've noticed the color of the leaves have begun to change to a lighter shade of green. Is this normal and if it is, is it time for me to switch to bloom fertilizer? Thanks for your feedback in advance!

 

[Anthem]

First off, there is no part of the plants life called PRE Flower. It is a term coined by people on the internet. You are in flower and your plants need more nutrients.