Map icons can use texture fills, for containers and agents the fill is used within the caption area of the icon but not the viewport. These textures are set via the $Fill attribute and the opacity of the fill texture can be further controlled by the $FillOpacity attribute.
If $NameColor (the colour of the title text) is set to the default of 'automatic') then the icon's title will be black or white text depending on the colour value of $Color and not the colour of the fill texture image. Thus if using fills it may be necessary to also set an explicit $NameColor value in order that there is sufficient contrast to read the title.
The texture is used to fill the whole face of notes and adornments. For containers and agents, the texture fills the part above/below the viewport as used for the title & text/table.
Built-in textures have the following name values:
Users can supply additional custom fill artwork; only JPEG format files are supported.