The ExComboBox control can group the control columns into two categories: locked and unlocked. The Locked category contains all the columns that are fixed to the left area of the client area. These columns cannot be scrolled horizontally. Use the CountLockedColumns to specify the number of locked columns. The unlocked are contains the columns that can be scrolled horizontally. To change the background color of the control's locked area use BackColorLock property. Use the BackColorLock property to specify the background color for locked columns.