Some credit card slips have a top sheet of “carbonless paper” that transfers an imprint of...

Some credit card slips have a top sheet of “carbonless paper” that transfers an imprint of your signature to a sheet lying underneath. The paper contains tiny capsules filled with the colorless compound shown below:

When you press on the paper, the capsules burst and the colorless compound comes into contact with the acid-treated bottom sheet, forming a highly colored compound. What is the structure of the colored compound?