I'm guessing all they mean is that dark to colorless is less subjective. Essentially it's easier to tell the difference and less risk of error. The solution either has a color or it does not. But, let's say your indicator goes from red (when basic) to yellow (when acidic). Your indicator (indi-) would be a in 1:1 ratio with H-indicator when the color is orange. But, I don't know about you, but in solution, red and orange can look pretty damn similiar. Thus, an indicator that goes from colored, to not colored makes detection much easier.
I don't know if this is what they were getting at but it was a good exercise for me anyways. My buffer and titrations knowledge needs the help.
