Paper reacts to pH, don't get me wrong . If you dip them in vinegar they will turn red, if you dip them in borax they will turn blue. The problem is, when you try to measure something that isn't a strong acid or base, the colors centered around the neutral point aren't that distinct! Especially with slightly acidic things, colors 4-7 are almost identical. The product page image was captured in a white field with bright white lighting which makes the colors in the photo easy to read, but in real life, under normal lighting conditions, colors 4-7 look and are the same shade of dull yellow also indistinguishable from the standard neutral paper color. So basically they're accurate enough to tell you it's either an acid or a base, but not the actual measurement, especially when they're close to neutral.
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