Anthocyanin

Anthocyanin is a plant pigment.  It is responsible for the purple flower color that is the most common among the so-called "unifoliate" Cattleya species (e.g., labiata, trianae, mossiae).  Besides its function in flowers, anthocyanin is produced and functions in other plant tissues including leaves and roots.  The result of this phenomenon is that Cattleyas that have unusually dark purple flowers also have more red pigment produced in other tissue types.  Here is an example of that.  This picture shows two views of a Cattleya labiata seedling I've been growing for about two years.  This plant is the rubra type, which has darker flowers.  The red pigmentation in the leaves is quite intense, especially on the undersides.  Plants that are alba or semi-alba often have leaves of a paler green compared to the typical form.