That range is from the BJCP style guidelines. Your wit is going to be too big for the style. You'll notice that Beersmith will boldface your OG until you get it into range (in the normal recipe creation screens).
Actually that is the gravity range for the particular bjcp style you are brewing. According to the BJCP a witbeer should have a gravity in the range of 1.042-1.055 to be true to style/
However your gravity (the number to the left of it,) is 1.072, which means your recipe it out of range and not true to style.