Is shell color in desert tortoises an indicator of anything?

[Bowi]

I’m new to desert tortoises and want to be sure I know. I notice some are tan and others shinier and darker

 

[Yvonne G]

In my experience, seems like the captive bred (tortoises who started life in an indoor enclosure, not exposed to the elements) are mottled brown, cleaner-looking. Not any kind of an indicator except for the shell hasn't endured the rigors of living in the wild.