I just started a goal with the week of flatness and my graph is blue, even though I'm nine days away from derailing! Also, I went on vacation a few months ago and put a few of my goals to zero while I was gone, and the colors for one goal told me I was going to derail even though I had a week and a half to derailment!

I think the "yellow brick road" analogy is okay, but it's just an analogy and adds an extra layer of interpretation in this and other cases (like the 0 safe day thing meaning that you've still got more than a day until derailment from your goal) that doesn't buy anything. Distance to the middle of the road is less useful than distance to derailment.

I really like the red=problem today, orange=problem tomorrow, blue=problem day after tomorrow, green=good for a few days (one weekend if it's Friday) that you get most of the time, but any time the future slope of the goal changes, the graph colors become useless.