I've learned a long time ago that there are a few things that could cause that: Nutrients, Humidity, DIstance between plants and light for light power, or it could just be the strain. 1 of my Zkittlez went to orange hairs from week 2 of flowering, It means nothing as long as it is still producing hairs, as it is the sac at the bottom of the hairs that ends up swelling near maturity, increasing size and density, the sacs also have the densest concentration of trichomes.