universal indicator
noun [ C ] chemistry specialized uk/ˌjuː.nɪ.vɜː.səl ˈɪn.dɪ.keɪ.tər/ us/ˌjuː.nɪ.vɝː.səl ˈɪn.dɪ.keɪ.t̬ɚ/
（化学上用的）通用指示剂（用来测定物质的酸碱性）
a chemical solution made from a mixture of substances that produce many different colour changes according to different pH levels, used to discover how acid or alkaline something is