Question

how indicators change the colour of acid and bases tell me briefly

Answer 1

The main indicators to test acids and bases are litmus paper i.e red and blue. when blue litmus paper are put inside acid then it turns red and when it is put inside red litmus then color doesn't change and when red litmus are dipped into bases then it changes it's color to blue.
I hope this helps

Answer 2

Indicators are used to detect whether a substabce is base or acid.Take an example of Litmus paper which turns Blue litmus to red when acid is treated and red turns blue when base is treated.