Combo Boxes final text value has to be on the list.

Hello all,

I cannot seem to find the answer that I am looking for so... I have a combo box with the DropDownStyle set to DropDown. I want users to be able to type and get the suggested options, but I do not want user's to type and leave a value that is not on the list. I have the SuggestAppend set for AutoComplete, but users can set the combo boxes text value to something that is not on the list.  Originally, I had the DropDownStyle set to DropDownList but the color change bothered me and all the solutions I found did not seem to let me change the BackColor. Can some please help me with getting the BackColor changed to "white" for a DropDownList  combo box or help me programically change the behavior of the combo box to not allow the value to equal something that is not on the list?

**Change the FlatStyle property to Popup is not an option.

Thank you for your assistance.
Shannon