Something like this works in c#:
protected override void OnBeforeEventRender(BeforeEventRenderArgs e)
{
if (Boolean.Parse(e.Tag["CheckedIn"]))
e.BackgroundColor = "#9FF59F";
if (Boolean.Parse(e.Tag["CheckedOut"]))
e.BackgroundColor = "#9BB3BD";
if (Boolean.Parse(e.Tag["ShouldBeCleaned"]))
e.BackgroundColor = "#FF9369";
base.OnBeforeEventRender(e);
}