You didn't say in your previous post if you'd selected a Theme for your control. Mine's been set to VisualStudio2012LightTheme
I tried your code and I'm MUCH closer which is great progress but I still have an unsightly white border that you can see in the attached image.
Here's the source for the test ap:
Private Sub Form1_Load(sender As Object, e As EventArgs) Handles MyBase.Load
' DropDownList1 has no Theme (or rather uses the Default)
RadDropDownList1.DropDownListElement.SetThemeValueOverride(Telerik.WinControls.Primitives.FillPrimitive.BackColorProperty, Color.FromArgb(226, 226, 226), "Disabled", GetType(Telerik.WinControls.Primitives.FillPrimitive))
RadDropDownList1.DropDownListElement.EditableElement.TextBox.SetThemeValueOverride(Telerik.WinControls.Primitives.FillPrimitive.BackColorProperty, Color.FromArgb(226, 226, 226), "Disabled", GetType(Telerik.WinControls.Primitives.FillPrimitive))
' DropDownList2 has VisualStudio2012LightTheme applied to it.
RadDropDownList2.DropDownListElement.SetThemeValueOverride(Telerik.WinControls.Primitives.FillPrimitive.BackColorProperty, Color.FromArgb(226, 226, 226), "Disabled", GetType(Telerik.WinControls.Primitives.FillPrimitive))
RadDropDownList2.DropDownListElement.EditableElement.TextBox.SetThemeValueOverride(Telerik.WinControls.Primitives.FillPrimitive.BackColorProperty, Color.FromArgb(226, 226, 226), "Disabled", GetType(Telerik.WinControls.Primitives.FillPrimitive))
End Sub
I can also see from your demo picture, you too have a 'light' border around your textbox (the color is 221, 231, 242)
Is there any way to change that color as well?
Thank you again for your help, Dess!
-Curtis