Answer the following question given this paragraph: 

Certain compounds, called indicators, change color when bases come into contact with them, so they can be used to detect bases. An example of an indicator is a compound called litmus. It is placed on small strips of paper that may be red or blue. If you place a few drops of a base on a strip of red litmus paper, the paper will turn blue. You can see this in the Figure below . Litmus isn’t the only detector of bases. Red cabbage juice can also detect bases, as you can see in this video: http://www. youtube. com/watch?v=vrOUdoS2BtQ .


Q: What kind of compounds change color when bases come into contact with them, so they can be used to detect bases?


A:
indicators