As Richard320 described the difference in chlorine levels. A funny but very accurate way to tell the difference. I don't know about you, but I have always had trouble with shades of color. Mauve is pink to me. Lime looks light green to me. And as I get older my vision is more questionable. This may not help you, but I have an lcd monitor on my shop computer on the work bench where I test my water and I have found that if I open notepad, the blank screen is bright enough and white enough that I can hold my sample a few inches away the screen and it really helps me with the subtle shade changes. Wish I could use that on the CYA test, if and when I get the TF-100 kit. Anyway for what it's worth, it helps me with color change tests. Hope it helps
