graduation
The color graduation of fillstyle. This is a graduation identifier.
If this value is not null it provides the background fill for the fillstyle, overriding any defined solid color fill (fillstyle.color), unless the fillstyle also contains an opaque tile pattern, in which any graduation is ignored.
For full color tile patterns, transparent images use fillstyle.color as the background, unless that color is null in which case the image tile is displayed transparent.
Note: fillstyle.tile and fillstyle.image are mutually exclusive.