Brown, Turtles in OK. or KN.?

I was on I35 north bound in OK.  Just south of KN.  When I seen a turtle almost across the Hy way.  Light brown sandstone colored shell.   I stoped grabed the camera,and went back to get a photo.  Could not find him. He had made the weeds along the ditch.  Could have been dirt stuck to shell. From being buried do to heat.  But has any one seen this color variation in turtles in that area??    Color not listed.

Maybe one of them