Depends on where these leaves are on the plant, that first pic is kind of overexposed so it's hard to tell. Lower sun leaves die off during flowering, very normal as the plant sends all it's energy to the flowers. IF you are having problems with the entire plant yellowing then you have other problems unless you're very close to harvest. If you're early in flowering maybe boost your nitrogen, fresh human urine diluted one cup to a gallon of water is a perfect source of nitrogen and is instantly available to your plant. You may also want to consider using molasses during the flowering stage.