Your CYA will not change color, the black dot on the bottom of the cylinder will disappear. This is one of the toughests test to get used to doing and the one that uses the most of your chemicals. But once you get your CYA correct you dont need to do it again but maybe once to adjust for evaporation, rain etc
My suggestion is to redo the test and see if you get the same results. If you TRUELY have no CYA in your water then you need to put some CYA or Stabilizer into your pool. You can get this at Home Depot , Lowes, Walmart in the pool section.
It would be helpful if you could add to your signature your pool size, make of pool (Vinyl, Gunite, fiberglass) the type of filter you have.
If you look in my signature you will see some helpful links to help you.