Apologies for my lies, or misinformation, whichever way you want to take it. Feel free to delete my previous comment mods. I was in fact referencing coachwhips, which are known to "stand" and run, which is sometimes thought to be chasing if cornered and can scare people because they are a large snake. You're correct they are tan or pinkish in SW Texas, but I have also seen them very dark closer to the river and north towards Big Bend. A lot of people in West Texas, in my little time around, call them black racers because they act similar to the eastern racer when they have such a dark color. My gf has been scared by the way they seem raise up and scurry away, but that's just my experience.