How do I change the color of a rdlc textbox

I'm using a rdlc report within a VB project.

I have a text field 'surname' and a boolean field 'sales'.

Depending on the value of the boolean field I want the text to be displayed in red or black.

Looking at examples I should be changing the text color.

But the label on the dialog box when I select 'expression' says 'Set expression for:Value' but I think I should be a able to select to set the expression for color.

I have the following expresion but it just displays the text "Black" and "Red" in the text box.

=iif(fields!sales.Value,"Black","Red")