In the lab, your tlc sheet is done and you have heated it with the hair dryer. if you have free amino groups (in amino acids) on your tlc sheet, the (chemical substance) in the solvent will turn orange, pink, purple or violet.

The given blank can be filled with ninhydrin.  

It refers to a synthetic crystalline component, which produces deeply colored products with primary amines and is utilized in analytical tests for amino acids. It is a chemical that is generally utilized to determine primary or secondary amines.  

In the ninhydrin test, the amines react with ninhydrin to produce a colored component. It can be used quantitatively (for peptide sequencing) or qualitatively (for chromatographic visualization). The alpha-amino acids usually give a blue-purple product.