Texas Indigos stay black, some even keep the red coloration on the chin and belly. Anyhow, they're protected here in Texas, we occasionally find them in the yard. Like DirtyBlackSocks stated; eastern hognoses are nice, I especially find the all black or menalistic hogs very attractive.
(i let the house cat, get a whiff of the snake.... snake was found in our yard)
You could also look for some really dark Cribos, those are something neat and big!