The yellowing is normal for all flowering plants...to a point. It increases starting about the 4-5th week until the end, with the buds staying green and juicy. The plant stops using N in this phase of life....essentially, not completely....and increases it's needs for P and K. That is why the leaves are yellowing.

Giving N at this point will make the end result nasty tasting, no matter how much you flush. As long as the buds stay healthy, who cares about the leaves. They still work for the plant when yellow.

Unsulphered Molasses can be given tho. Won't make the sun leaves green, but will give nutes they need in a natural way.