Yehuda is a company with an excellent reputation that sells clarity enhanced fracture filled stones.
These are stones which formerly are usually very imperfect to the eye, with surface-reaching fractures that show up as large white feathers when not treated.
They are treated by putting them in a vacuum, and sucking a molten glass-like resin down in the fractures. The glass has a closer refractive index to the diamond than air, and consequently renders the fractures almost invisible to the eye.
These stones can be quite nice looking, at very reasonable prices. There is definitely a place for them in the market for someone who wants a good looking diamond at a bargain price.
The things to be aware of are the durability factors. Large surface reaching feathers make a diamond less durable than one that doesn't have them. This is usually not a problem, but sometimes can be if the diamond takes a sharp blow in one form or another. The possibility of it cracking are significantly greater than non-enhanced stones.
You have to also warn any jeweler about to work on it that it is a Yehuda stone, and not to put the high temperature of a torch to it. The glass will melt and come out, reverting the stone back to it's original appearance.
This would not be the end of the world though, because Yehuda extends a lifetime guarantee to re-enhance any of their stones at no charge.
I would say if you like it, and don't mind the cautions, to go ahead and buy it. You'll get many years of pleasure out of owning a beautiful diamond which "only your jeweler can tell for sure".
