If you click on Report – then Report Properties in the menu (assuming you’re in BIDS) and choose the ‘Code’ tab. Now, before we start, it’s best to point out that this is not a normal code surface – pretty much only a textbox, so there’s no intellisense, so you’ll need to know what you’re doing.
Here’s a code sample you can go by:

Function ColorStyle(ByVal Style As String) As String
        Select Case UCase(Style)
            Case "HEADER"
                Return "LightBlue"
            Case "FOOTER"
                Return "Blue"
            Case "SUBTITLE"
                Return "DarkBlue"
        End Select
    End Function

Note that these can easily also be the normal HTML hex numbers you might be used to.

To use this function, you will click on the color property in the property view which you need to use it with, such as the Backtround color of a particular control. Instead of choosing a color from the list, you’d type in something like:

=code.ColorStyle("Header")

Of course, you’ll see the results when the report is actually run.