Hello, Wojciech,
Thank you for writing.
In
RadMultiColumnComboBox you have direct access to popup grid by the
EditorControl property. Thus, you can use the API that
RadGridView offers for customizing the cells. You can either use the
CellFormatting event or benefit from the
conditional formatting. Feel free to use this approach which suits your requirement best.
I hope this information helps. Should you have further questions I would be glad to help.
Regards,
Dess
Progress Telerik