That's the system highlight color (SystemColors.Highlight). It changes based on your system settings and theme so it's not always blue, although that's the default. 

It only highlights the whole control like that when DropDownStyle is set to DropDownList.This is standard behavior for all ComboBox controls in DropDownList style in DotNet.

There is no property to change this color on any control (including the MS ComboBox) as far as I know.

But you could change the colors on the Infragistics control by using a DrawFilter.

I am trying to remove the microsoft 'blue' background color from ALL of the controls. but for the purpose of this discussion, let's just talk about the UltraComboEditor

msft=microsoft