InlineUIControl

Question

Hi.

I have a project in wich I must create a form editor (just like infopath) using wpf. For this I thought to use a RichTextBox and in there I would place InlineUIElements with the different controls (TextBox, ComboBox, etc.). The problem is that I can't change some properties associated with those controls. Here's some XAML:

<RichTextBox>
    <FlowDocument>
        <Paragraph>
            <InlineUIContainer>
                <TextBox Background="Red">Some Text</TextBox>
            </InlineUIContainer>
        </Paragraph>
    </FlowDocument>
</RichTextBox>

This displays a TextBox in a RichTextBox just like I wanted but it's not red. Some other properties work like width and height.

Why is this and how can I make it work?

Other question is: Am I approaching the problem (creating the form editor) right?

Thanks