well yellowing leaves is normal during flowering, i believe. you can supplement that by making sure your fertilizer has lots of nitrogen in it. my plants are actually doing the same thing, but the leaves are yellowing quite rapidly and dying off. i still haven't quite figured it out, i have tried lots of nutes, and no nutes and it hasn't seemed to help yet. but try the extra nitrogen and see what happens. posting some pics of the yellowing leaves will help us out too.