ceres purple strain

My last harvest my purple plants didn't turn purple im on my second grow now im 2 weeks into flowering what can I do to make my purple plants turn purple

lower temperatures slowly to around 68-75 degrees. low temps bring out purple in predominantly purple strains better than those that are not, watch your plant and find the temp it starts to change at, that is where you should keep it, as low temps can stunt, or lower potency.