The great thing about the genus Thamnophis is the variety within the different species. Accidental crossings have happened and to be blunt the snakes looked like washed out mixes.
There is a great debate as to what should be done with the mutt offspring. They are detrimental to the gene pool.
Crossings due happen in overlapping ranges for some species but even that has never produce some wild looking snake.
If you want an awesome looking snake stay with a species or subspecies please.