I live in Indiana and I know the commons around here have various shell and skin colors. I always catch a lot of hatchlings/yearlings down at a golfcourse where the soil is real dark, and thier always almost black in color. I also find a lot more lighter colored red/tan ones in a different location where the soil is made up more of sand and clay... Seems to prove true.

-Chris
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Currently in the US Navy so I have sold off my collection. But over the years I have had dozens of turtles, fish, geckos, and other lizards. Cant wait to get back in the hobby once im out though!