Hardwood flooring is a truly organic material.
This picture illustrates the intriguing 'Leopard Spots' that can present in the African Wenge hardwood.
Every tree is a unique individual that is affected by environmental conditions ranging from soil structure and mineral content to solar radiation input and moisture levels. Often the anomalies that occur in a wood floor are what makes it so interesting.
These spots are variations in the fiber structure of the tree. Once the tree is milled into boards, these anomalies appear as distinct colour differences. Even after finishing, these "spots" are still visible.
When you are choosing a wood floor for your project, it is important to understand that exotic woods, as well as some species of domestic, can exhibit unique characteristics.
Plan ahead. If you are not willing to accept variation, then more flooring should be purchased in order to "cull" some of the non-desirable traits.