Function layoutBackgroundSysVar

layoutBackgroundSysVar(isModelSpace: boolean): string
Returns the layout-background system-variable name for the active space.

AutoCAD stores separate background colours for model space and paper space:
- Model space — AcDbSystemVariables.MODELBKCOLOR
- Paper space — AcDbSystemVariables.PAPERBKCOLOR
Parameters
- isModelSpace: boolean
  true to target model space; false for the active paper-space layout.
Returns string
The sysvar name string passed to AcDbSysVarManager.
Example
```
layoutBackgroundSysVar(true)  // MODELBKCOLOR
layoutBackgroundSysVar(false) // PAPERBKCOLOR
```
See
- readLayoutBackgroundColor — reads and resolves the colour value
- AcApSwitchBgCmd — toggles the sysvar via this helper
- Defined in packages/cad-simple-viewer/src/editor/global/AcEdUiColor.ts:136