Do any of the following:
Change the outline: In the Table Outline section of the sidebar, use the controls to change the line type, thickness, and color.
Change the gridlines: In the Gridlines section of the sidebar, click the buttons to show or hide gridlines from the table body, from the header rows and columns, and from footer rows.
You can change the border and background of any selection of table cells.
Go to the Pages app
You can also create rules to automatically change a cell’s look when the value in the cell meets certain conditions. See sidebar, click the Table tab.
In the sidebar, select the Alternating Row Color checkbox, then click the color well to select a color.
Row colors don’t alternate for header columns. Header columns have their own look based on the table style you choose.