To hide the lines in the spreadsheet grid, simply select 'Hide Grid Lines ' under the 'View' option in the main menu, located near the top of the SpreadsheetLIVE user interface. Once they are hidden, the option will change to 'Show Grid Lines', if you decide that it's preferable to see the grid lines.
Image 1 - The 'Hide Grid Lines' option under the 'View' menu in the main menu bar.