You either have to have far better color vision than I have, or most of the nitrate readings you get are at least 50% imagination, even if the test kit is still working right, and you are using the kit correctly. The best I can do with that kit is to say I have somewhere around 20-40 ppm, or 40-60 ppm, etc. It is a lot like measuring pH with an API style test kit. And, I'm not at all color blind.If the nitrates are from fish food then there may be other things in the water that you want to remove. Do water changes, feed less.
If the nitrates are from fertilizer you are over fertilizing.