<html><head></head><body style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space; ">I'm sorry I wasn't able to get to look at this carefully until today.<div>I literally copied your code below into a tex file and ran it on my machine. The outcome differs from yours (yours is what I would want---or at least what I could work on to get what I want).</div><div>The difference is the printing of the black hyperbola on the upper gray plane. </div><div>My code and output are attached; any idea what might cause the difference?</div><div></div></body></html>