Reading Salifert copper test

[Areseebee]

I really hate colorimetric tests, I can't figure out if it's just some deficiency I have or it's this useless to everyone. I bought the Salifert copper test to precisely ensure I don't overdose copper, so I add it slowly and test. The result of my current tank are below. I'm aiming for 0.5, 1 is apparently deadly, the colors range from grey to purple and the test is blue. No idea how to read this.

 

[Areseebee]

I made a standard the other day by trying to do exactly one drop in 1/4 gallon (which should give 0.5) but the lighting is different enough that the standard isn't really helpful.