Sadly, this is not true, as I mentioned here. You can easily have a green goal with less safety buffer than an orange goal. I don’t mean to nitpick you, but I want to try to be as accurate as possible when there are Newbees around. 
EDIT: The reason is that the colors are computed based on a concept of “lanes” and whether you are in the “right lane” or the “wrong side of the road” or “off the road”, etc. But these don’t translate directly into a number of safe days whenever the road slope changes, most often due to a derail. This is also why brand-new goals start in the blue despite having a week of safety buffer!
EDIT2: Heh I also notice that just by sheer good luck, my image above of the 8 days safety buffer is in blue.