X-GAL
Thermo Fisher ScientificX-GAL (5-Bromo-4-Chloro-3 Indolyl-Beta-D-thiogalactopyranoside) is a chromogenic substrate for Beta-galactosidase that turns blue upon hydrolysis and is regularly used for the blue/white color selection assay. Bacteria with a lac+ phenotype grow as blue colonies on plates containing X-GAL.