The onBeforeCellRender event is fired once for every cell during rendering. You can use it to customize the cell appearance.
DayPilot.Month.onBeforeCellRender(args);
Cell properties (args.cell.properties):
The args.properties object is available since 2021.4.5146. In prior versions, these properties are available directly in the args.cell object (e.g. args.cell.cssClass).
dp.onBeforeCellRender = function(args) { if (args.cell.start.getDayOfWeek() === 6) { args.cell.properties.backColor = "#eeeeee"; } };