Thanks for the writing.
In case that you want to set the back color of the text box hosted in RadDropDownList you should use the following code snippet:
.radComboBox1.DropDownListElement.TextBox.Fill.BackColor = Color.Red;
.radComboBox1.DropDownListElement.TextBox.BackColor = Color.Red;
.radComboBox1.DropDownListElement.EditableElement.BackColor = Color.Red;//For DropDownStyle = DropDownList
This can be also set via Visual Style Builder
I hope this helps.
the Telerik team
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