What aspect of a diamond can be dramatically affected by fracture filling?

Fracture filling is a process where a substance is used to fill in cracks or fractures within a diamond. This treatment can significantly enhance the apparent clarity of the diamond. When fractures are filled, they become less noticeable, which means the diamond may appear to have fewer inclusions and blemishes when viewed under standard lighting conditions.

This improvement in how the diamond looks to the eye directly impacts its clarity grade as perceived by consumers and appraisers. In many cases, this treatment allows diamonds with otherwise poor clarity ratings to present themselves as having higher clarity, making them more appealing in the market.

While other aspects like color, cut, and carat weight may also be factors in a diamond's value and appearance, they are not directly influenced by the act of filling fractures. The enhancement of clarity is the primary focus of fracture filling, making it the most appropriate answer to this question.