what does white pony mean?

We got the answer, straight(ish) from the horse’s mouth

IS THE TITLE A REFERENCE TO DRUGS?

“Honestly, it didn’t start as a from it or whatever. I always found it very ambiguous. I found more excitement in people trying to understand what it was, and then come in with their own ideas. And then I would just go ‘Hmmmmm yeah, yeah OK, maybe…’ and never confirm anything. I enjoy the ambiguity of it. If anything, that’s how I’d always perceived it.”