加酸显色材料（halochromic material）是一种会随着pH值改变而改变颜色的材料。其英文本根「chromic」，即「着色异常」指的是会因为外在参数的改变而改变颜色的材料。在这里，这个参数即是pH值。而酸碱指示剂就是利用这种特性制成。

A halochromic material is a material which changes colour when pH changes occur. The term ‘chromic’ is defined as materials that can change colour reversibly with the presence of a factor. In this case, the factor is pH. The pH indicators have this property.