ELOS Test kits - when is "yellow" considered "yellow"?
 

On the Alk Elos test kits, it says to add drops until it turns from cyan to yellow.

Well it first turns slightly green, then greener, then even more green, then greenish yellow, then greener yellow, then even more greenish yellow then it turns yellow.
Theres about 5-6 drops difference in the color change which is equivalent to 2-3 dkH
At what point do we we make the reading?

I always do it in the same light... for whatever reason I'm confident that what I've chosen as yellow is very close each time. If you add one more drop to your yellow and it looks yellower still... I don't think you were quite there.

thats the same rule i go by as well

My opinion
 

Yes you need good light & when I test I always hold the testing tube up in front of a white back ground so the color reads true. As you mentioned, you will find that when it first changes to yellow it is rather a pale color and 1 more drop (.5 DKH) makes it brighter. That said whether you read it as pale yellow or bright yellow will only be .5 DKH difference so it is with tolerences but which ever way you read it the important thing is to try and be consistant and always read it that way. Once you test enough with it you can judge from the shade of the greenish yellow color how many more drops it would take to turn it true yellow and not even waste them on that test saving more for later. :wink: