Changing color in a paragraph

I am attempting to change the color in a paragraph but only part of the paragraph.

Here is my code behind example...

slides(0).Shapes(2).TextFrame.Text = "Username = " & Me.lblUser.Text

slides(0).Shapes(2).TextFrame.Paragraphs(0).Portions(0).FontColor = Color.Red

I want the user to be in red but not the first part, "Username = "

So it would read "Username = Todd"

How can I do this in the code behind ( The above code changes the entire line red.

Dim pres As New Presentation
Dim sld As Slide = pres.GetSlideByPosition(1)

Dim rect As Aspose.Slides.Rectangle
rect = sld.Shapes.AddRectangle(500, 500, 3000, 2000)
rect.LineFormat.ShowLines = False

Dim tf As TextFrame = rect.AddTextFrame("")

'The relevant code starts from here
Dim para As Paragraph
para = tf.Paragraphs(0)

Dim port As Portion
port = para.Portions(0)
port.Text = "Username = "

'Now the red colored name
'to do so, you will add a new portion object
'portion object is the object that holds indvidual textformatting
Dim newPort As New Portion(port)

'Set the text and color of new portion
newPort.Text = "Todd"
newPort.FontColor = Color.Red

'Write presentation on disk