src/vs/platform/theme/electron-main/themeMainService.ts/ThemeMainService/updateBackgroundColor
class ThemeMainService:	private updateBackgroundColor(windowId: number, splash: IPartsSplash): void {
		for (const window of BrowserWindow.getAllWindows()) {
			if (window.id === windowId) {
				window.setBackgroundColor(splash.colorInfo.background);
				break;
			}
		}
	}