Gaia colour-magnitude diagram. Full blue circles show composite-spectrum sdB+MS binaries and empty blue circles show the single-lined sdB+MS binaries. sdA+MS binaries are similarly coded in green circles. The systems that will form an sdB+MS or sdA+MS binary are shown with orange squares at the moment when the interaction phase starts. As a comparison, the Gaia colour-magnitude diagram of the HIPPARCOS sample is shown in grey.