ASEAN is not a country it is an acronym for the Association of Southeast Asian Nations.
The flag is based on the ASEAN emblem. In actuality the emblem is circular and bears the letters ASEAN in a lowercase type face.
The flag has a blue background and the emblem is circular with a red center and a thin white ring around the red and then a blue ring around the white. There are ten stalk tied together which stands for the found fathers of ASEAN’s dream of having all ten Southeast Asian countries part of the organization.
Blue stands for peace and stability, red symbolizes dynamism and courage. Yellow denotes prosperity and white portrays purity.
The rules that govern the manufacturing, use, displaying and bearing are very specific and detailed. Even the dyes used to create the different colors are specified.
For instance if blue Pantone 286 was the shade chosen for the blue in the flag, that same blue must always be used.