In the [Basic] tab, if you clear the [Show
Fill] check box the top 8 bits of the [Display Color] address store
the color code for the background color.
19.12.1.1 Normal Graph -
Basic
When using a pattern, if you set the [Pattern
Color] to [Black] (or color code 255) and [Blink] to [Medium], the
display will become transparent and may not show correctly. The
same is also true when [Pattern] is [None], and you set [Background
Color] to [Black] (or color code 255) and [Blink] to [Medium].