Yellowing is normal in flowering, but it looks like your plants are suffering from more than N-deficiency in flower judging by those scorched looking blotches. Are you watering with distilled or otherwise purified water? It almost looks like you have a bit of a Calcium deficiency, but it's hard to tell without knowing more about your setup, nutes, etc. Fill out the Troubleshooting Form, and you will be able to get more tailored advice for your plants.