To change any cell background color, use the following code in the After Record Processed event.
record("FieldName_css") = "background:red;"
You can also change the background color of a cell when the mouse hovers over it:
record("FieldName_hovercss") = "background:yellow;"
See also:
•Change the row background color
•Grid Row JavaScript API: row.fieldCell()
•About Grid Row JavaScript API