Blue zones were areas of the Earth suffering the least ecological damage from Tiberium after the Second Tiberium War. Compared to the yellow and red zones there was minimal Tiberium contamination and war. Tiberium growth was countered and controlled by harmonic resonance technology. Blue zones were attacked in the opening of the Third Tiberium War by Nod, and later by the Scrin attempting to draw attention away from the Threshold towers. By the end of the Third Tiberium War, there were only 19 blue zones left.