Try looking at the test tubes from the top down. You're looking through the entire tube so the color is more intense.
I agree these are hard to read. I have problems with color blindness - and because these are orange/green it certainly isn't easy for someone with a red/green deficiency which I believe is one of the most prevalent cases of color blindness.
I have found though, that after several drops there will become a definitive change... I just usually start off adding 3-5 drops right away, knowing that I'm not going to see a change.