Good point, Kevin--you're right.
But perhaps, in the interest of staying true to the basic universal and "official" definition of black diamond as "most difficult," we should quibble with the phrasing. If black diamond means most difficult, then "easy black run" means "easy most difficult run"--a literal self-contradiction and oxymoron if there is one!
You're right though, of course, that black diamond difficulty encompasses a wide spectrum, both within a ski area, and even moreso, from one ski area to another. So it is a very reasonable for someone trying to become familiar with a new resort to want to know where to find the least or most challenging runs within that spectrum. Asking "how do I get to the least challenging black run?" would get the point across, while eliminating the oxymoron that there should be any such thing as an easy difficult run.
There are also things like "steepest green run"--which may be of critical importance for beginning skiers to know! (Hint: if you can just survive the steepest parts of "Schoolmarm," you might want to hold off a bit before you tackle Snowbird's Big Emma!)
But how would you describe the "most intermediate blue run"? How about "Extremely intermediate?
Well, the "most intermediate blue run" is the extraordinary one. Extraordinary = extra ordinary = extremely normal. Gotta love the English language.