Syntax:
set style fill {empty | solid {<density>} | pattern {<n>}}
{border {<linetype>} | noborder}
The default fillstyle is empty.
The solid option causes filling with a solid color, if the terminal supports that. The 5#5density6#6 parameter specifies the intensity of the fill color. At a 5#5density6#6 of 0.0, the box is empty, at 5#5density6#6 of 1.0, the inner area is of the same color as the current linetype. Some terminal types can vary the density continuously; others implement only a few levels of partial fill. If no 5#5density6#6 parameter is given, it defaults to 1.
The pattern option causes filling to be done with a fill pattern supplied by the terminal driver. The kind and number of available fill patterns depend on the terminal driver. If multiple datasets using filled boxes are plotted, the pattern cycles through all available pattern types, starting from pattern 5#5n6#6, much as the line type cycles for multiple line plots.
The empty option causes filled boxes not to be filled. This is the default. It is equivalent to the solid option with a 5#5density6#6 parameter of zero.
By default, border, the box is bounded by a solid line of the current linetype. border 5#5lt6#6 specifies that a border is to be drawn using linetype 5#5lt6#6. noborder specifies that no bounding lines are drawn.