Shorter wicks really help, too. The 'problem' juices will turn dark in the atomizer cup and then leach back down into the tank through the long wicks. You can actually see it happening in the beginning, just the wick is darker. Anyhow, go old-style 'ears' with your wicks. Trim them so they protrude enough to touch the side of the tube. You'll need to tip-n-roll more, but it will keep your juice clearer. The juice in the atomizer head will still go dark, but it can't run down back into your tank as easily.
On other juices, long wicks aren't an issue and I keep them long.