This is because pH indicators, which are substances that change color depending on the acidity or alkalinity of a solution, are designed to show a specific color at a neutral pH.

Common pH indicators and their colors at neutral pH:

* Universal indicator: Green

* Litmus paper: Purple (though it's not actually green, it's close to neutral and often used as a visual cue)

Keep in mind that the exact color might vary slightly depending on the specific indicator used and the concentration of the solution.