Unless you are in a hydrohut, I wouldn't worry too much about it....I have run the gambit of yellowing problems, staritng in a damn hydrohut and beyond, and my ladies are doing fine now. Temps will also effect color of new growth. Try to get temps as stable as possible, definitely without serious fluctuations, as they will discolor from that ( I know from experience). Here is a link I love to share, which has helped me alot.
International Cannagraphic Magazine Forums - The Complete guide to Sick Plants,pH, and Pest troubles!