MSU, along with a lot of baseball teams (high school, college and pro [all the MLB teams started using it 20 to 25 years ago]), are using a clay material called Turface as the cover for the sand and dirt used on their infields. MSU, which has been using it for years, is currently using a lighter color Turface to cover the infield. They will be going to a more brown color, very similar to what the new artificial surface base paths look like.
BTW, Coach Cohen showed me a picture of the new Turface that MSU is going to be using next season. I actually thought it was a picture of the new base path infield initially because it was so similar to that color.
Turface is used for several reasons. According to the Turface website, Turface "maintains a smooth, cushioned, playable surface for superior traction and player safety, absorbs excess moisture and improve drainage as a result of balanced air and water pore space, fights infield compaction that leads to running, sliding and bad ball hop injuries (and is) ideal for new infield construction or renovation."