Hello, Curtis,      

RadDropDownList hosts the standard MS text box when the DropDownStyle property is set to RadDropDownStyle.DropDown. I supposed that you have already found the following article since the provided code follows a similar approach: https://docs.telerik.com/devtools/winforms/telerik-presentation-framework/override-theme-settings-at-run-time


After I apply the following code snippet, the disabled state of RadDropDownList looks like the screenshot below:



I hope this information helps. If you have any additional questions, please let me know.  
Regards,
Dess
Progress Telerik

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

 

 

Hello, Curtis,      

For the VisualStudio2012Light theme you can use the following code snippet:




I hope this information helps. If you have any additional questions, please let me know.  
Regards,
Dess
Progress Telerik