Maya blue is a pigment invented by the indigenous people of Mesoamerica. It is a hybrid material that fuses botanical indigo to an inorganic clay. It has been used by indigenous people for hundreds of years. Maya blue can still be seen in the murals at Bonampak in Chiapas. These murals date to the late 8th century. It was also used by indigenous painters, like Juan Gerson, in painting the walls and ceilings of churches. The Mesoamerican Codexes, both pre and post colonial, contain Maya blue in the illustrations. The blue/turquoise color is still bright in all of these examples.
When indigo is fused to the clay it becomes much more lightfast and resistant to changes in pH. Western scientists are still working to decode the complete molecular structure of the pigment. Palygorskite and sepiolite are the best clays for making Maya blue. They have a unique molecular structure with niches that can enclose the indigo molecules.
The ratio of clay to indigo depends on the strength of the indigo powder and the color the artist wishes to achieve. Lower concentrations of indigo are the most stable as excess indigo powder will not bond to the clay and instead be left in the pigment as free indigo. If you want to learn more details about the process of making Maya blue you can purchase the recording of my class from Plants and Colour's series of online classes with different artists. It will be available for the next 2 months.
If you have seen other "Maya" pigments, such as Maya red, these are made by fusing synthetic dyes with palygorskite. To date I have not been able to find information about successfully bonding other natural dyes to palygorskite. The particular size and shape of the indigo molecule fits into the clay niches and is able to form chemical bonds with the clay. Modern scientists are certainly interested in creating other pigments in this way and there will likely be more developments in the future.