Adjust KI concentration with water to control speed of color change. Dog's toe nail clippers work well in cutting off small amounts of endosperm from the seed.
Tincture of iodine works well, and can be bought in drug stores.
Glume awn length may also be influenced by this gene. In black lines Pre2 is visible only just prior to development of black pigment. Check for it regularly where you only have one or two heads per plant. Under poor growing conditions, as is often found in greenhouses, there may be few or no seeds set in the lateral florets of some of these lines. The Zeo Zeo head is very short, as compared to the normal.