Having owned three of the four types of white snake - BluEL, Ivory, and BlkEL - I will tell you that every BluEL will develop some kind of stripe and will yellow up some, it is inherent to the mutation. Granted it is more faded in some than others but all of them have it. As Del said, the Hypo Butter/Mojave is probably your best bet but I had a 2000g female of that exact combo and she definitely had a stripe that you could make out.
If you want a truly eye-blindingly stark white snake then your best bet is an all-white BlkEL or all-white Pied. My SuperFire SuperPastel YB girl made my Hypo Butter/Mojave ad my Ivory Butter OD Pastel look dingy