How do Blue potatoes differ from Yukon Gold potatoes? In what ways do Blue potatoes differ from Yukon Golds?  (Other than the color.)  


Do they have comparable amounts of starch and water?
Do they have a different flavor or texture?
How should I be prepared adjust my cooking method if substituting Blues for Yukons?
There definitely is a difference in flavor, although it is rather subtle. I find that the blue potatoes are a touch richer or more "potato-y" than Yukon Golds. However, in cooking with them I've had plenty of success doing direct substitutions. Other than the blue color being a little odd-looking in some recipes I think you'd be safe just swapping one for the other in most cases.