Colour-magnitude diagrams - in which the absolute magnitude (Mv) of a selection of stars is plotted against their colour (B-V) - are frequently used in determining fundamental properties of the stars, and are commonly used as a teaching tool for explaining stellar evolution.
In this latter context, Andrew Gould has created an Hipparcos colour-magnitude diagram (see above) that is colour-coded by transverse velocity, the latter derived from the Hipparcos proper motion measurements. The data are selected to ensure the inclusion of a good sample of luminous stars, a representative sample of local stars, and most of the halo stars observed by Hipparcos.
Colour-coding the data according to the transverse velocity of the stars reveals the connection between the photometric and kinematic properties of the local population. Younger stars, typically found early on the main sequence, tend to move slower than later main sequence stars, which are mostly older. See astro-ph/0403506 for a more thorough description of this figure and details on its interpretation. (A high-resolution image is also available there.)
Gaia's precise astrometric and photometric measurements for more than 1 billion stars in our Galaxy, and beyond, will result in improved constraints on models of stellar evolution.
Image courtesy of Andrew Gould.