Cinnab is a term from the pallet system of non-binary gender presentation. It's used to describe non-binary people's gender presentation without having to use the binary language like "masculine" or "woman-aligned". It is similar to the lesbian terms "butch" and "femme". The term was designed to be used along side the galactian alignment system, but can be used by any non-binary person. For example a masculine and androgynous presenting, masculine aligned non-binary person could call themself cinnab solarian.
The flag was designed by Tumblr user Elfiot, the coiner of the term, in January 2018.
Cinnab is derived from the word cinnabar, which is a shade of red.