Change BackColor of Cell in Month View

Hello, Martin,     

According to the provided information, it is not clear how exactly you are trying to customize the month cells. However, I suppose that you are handling the CellFormatting event and setting the CellElement.BackColor property to White. This seems to work as expected on my end with the ControlDefault theme:

Please make sure that the DrawFill property for the CellElement is set to true: 

        public RadForm1()
        {
            InitializeComponent();

            this.radScheduler1.CellFormatting+=radScheduler1_CellFormatting;
            this.radScheduler1.ActiveViewType = SchedulerViewType.Month;
        }

        private void radScheduler1_CellFormatting(object sender, SchedulerCellEventArgs e)
        {
            e.CellElement.BackColor = Color.White;
            e.CellElement.DrawFill = true;
            e.CellElement.GradientStyle = GradientStyles.Solid;
        }

If you are still experiencing any further difficulties, it would be greatly appreciated if you can specify the exact steps how to reproduce the problem. Once we replicate the issue locally, we would be able to investigate the precise case and assist you further.

I hope this information helps. If you need any further assistance please don't hesitate to contact me. 

Regards,
Dess | Tech Support Engineer, Sr.
Progress Telerik