When the indicator was added to the solution, the color changed at once.
Tips
usage
Standard chemistry-class term: 酸碱指示剂 'acid-base indicator', 氧化还原指示剂 'redox indicator', 淀粉指示剂 'starch indicator'. Compare 试剂 (shìjì) 'reagent' — broader, any chemical used in a test, not specifically one that signals a result by changing color.
