Function Description:
The HPBACKGROUNDCOLOR system variable is set the background color of hatch pattern.
Type : Strings 
Saved in : Registry 
Initial value : None
Valid values:
"None" or "." to apply no background color Index Color: an integer between 1 and 255, or color name of the front seven colors
True Color: a RGB or HSL value between 000 and 255, the format is "RGB:000,000,000"
Color Books: standard color system, wizard, and set text 
											  Article ID: 1613
											  Created: July 16, 2021
											  Last Updated: July 16, 2021
											  Author: GstarCAD MY /KW
											
Online URL: https://kb.gstarcad.com.my/article/hpbackgroundcolor-system-variable-1613.html