Block Documentation - minecraft:map_color
minecraft:map_color is a
String component that sets the color of the block when rendered to a map. The color is represented as a hex value in the format
#RRGGBB. May also be expressed as an array of [R, G, B] from 0 to 255. If this component is omitted, the block will not show up on the map.
Default Value of the Component
This component is specified as a
Hex String to describe your color of choice, so there is no default value. You must provide a valid hex string in order to use this component. If this component is omitted, the color shown on the map will be that of the block below it.