I don't know if anybody else does this but with a glass CO2 drop checker it is very hard to discern the color of the DC solution while in the tank.
What I do is take a small very fine threaded WHITE fish net and use it as a background when I want to check my DC solution color. I find it helps ALOT in seeing the shade of green the DC is displaying. A whit e background iseems best to me. Especially for the dual chamber Cal Aqua Labs DC where you are comparing 2 colors.
What do you guys use as a background?