this will not work i am sorry to say. i used to put two gatorade bottles with frozen water into my res keeping the water at around 55 degrees and still no color. i did it b/c of the heat in my room was heating up my res and messin with the roots. also putting just plain ice in the res will throw off the PH as it is just plain water, thats why i put in frozen gatorade bottles. good thought though. the food coloring idea i believe would not work. i read that theory on OG a while back and it turned out that roots only take up water and nutrients, not anything with a flavor or color to it. remember if the bud yorue growing is tasty and potent enough the purple doesnt even matter. as latewood said the color has nothgin to do with taste smell or potency.

cheers,
money shot