This sample shows how you can customize the workbook background.
You can set the background color or background image for every sheet with backColor or backgroundImage. If you set both the backcolor and background image, the background image is displayed.
var spread = GC.Spread.Sheets.findControl(document.getElementById('ss'));
spread.options.backColor = 'red';
// The backColor will work if the backgroundImage is not set.
spread.options.backgroundImage = 'images/backImage.png';
SpreadJS provides the ability to control the image layout with backgroundImageLayout. The image layout contains the following types:
spread.options.backgroundImageLayout = GC.Spread.Sheets.ImageLayout.stretch;
You can also set background color for the gray area which is behind the sheet with grayAreaBackColor.
spread.options.grayAreaBackColor = 'gray';