The default display in Meshmixer is not ideal for working with technical models.

The setting responsible for this silliness is called "Mesh Normal Mode", which is unclear to most people who are not professional graphics programmers. Set that to "Face Normals" and it will display without making the model look like an amorphous blob. Alternately, hold spacebar and select the sphere that has vertices as in the picture below.

Setting in the "Hotbox"


Face Normals