I have an ant question!
My son's Uncle Milton Gel colony has developed a dark spot towards the
top. On one side, it looks almost white. On the other it looks
brown. It is rather large and appears to be slowly growing. Can you
tell me what this is?
Without being able to see the spot, I can only take an informed guess. My suspicion would be that the spot of discoloration is growth of a bacteria and/or mold.
Has your son added any food to the farm? Adding food can cause molds or bacteria to grow more quickly. Even without added food, the ants bodies/by-products can start a bacteria or mold colony growing in the moist, nutritious gel. Sometimes the contamination can simply come from particles in the air that land on the surface.
In any case, if your son's ants are not too active, you might want to try scooping out the discolored area as much as possible with a clean tool. If the ants are active and healthy, they may try to remove it themselves.
You can also wait and see what happens. It's possible the mold or bacteria will not harm the ants, or the ants will not survive long enough for the spot to become an issue.